Build a static binary

I recently tried installing the program via Homebrew on a machine that
didn't have 'libgit2' installed. The Homebrew formula installs pre-built
binaries. Running the binaries gave me an error saying that the
'libgit2' dynamic library couldn't be found.

Change the build configuration to build a "static" binary. It still
links to system dylibs, but I've removed all links to Homebrew dylibs.
These were:

* libgit2
* openssl

Removed the 'openssl' link by adding the 'vendored-openssl' feature to
the 'git2' dependency.

In order to remove the 'libgit2' link, I had to do some more finagling.
Accomplished this by setting an empty `PKG_CONFIG_LIBDIR` when building.
While 'git2' doesn't have a Cargo feature to disable dynamic linking, we
can force static linking by preventing `pkg-config` from finding the
Homebrew-installed 'libgit2'. The 'libgit2-sys' crate's build script
first checks for the library using `pkg-config`, and builds it
statically if it doesn't exist:

https://github.com/rust-lang/git2-rs/blob/43d583fd8b50fad0cfe0bbc334059ce965b6f3fc/libgit2-sys/build.rs#L15-L17

With these changes, the above packages will now be statically linked
with the program's binaries.

Upgrade 'git2' to the latest version (0.13.11) since we're changing its
build configuration.

Before:

    $ otool -L target/release/git-sug*
    target/release/git-sugapply:
      /System/Library/Frameworks/Security.framework/Versions/A/Security (compatibility version 1.0.0, current version 57740.60.18)
      /usr/local/opt/libgit2/lib/libgit2.1.0.dylib (compatibility version 1.0.0, current version 1.0.1)
      /usr/local/opt/openssl@1.1/lib/libssl.1.1.dylib (compatibility version 1.1.0, current version 1.1.0)
      /usr/local/opt/openssl@1.1/lib/libcrypto.1.1.dylib (compatibility version 1.1.0, current version 1.1.0)
      /usr/lib/libz.1.dylib (compatibility version 1.0.0, current version 1.2.8)
      /usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1238.60.2)
      /usr/lib/libresolv.9.dylib (compatibility version 1.0.0, current version 1.0.0)
    target/release/git-sugapply.d: is not an object file
    target/release/git-sugdiff:
      /System/Library/Frameworks/Security.framework/Versions/A/Security (compatibility version 1.0.0, current version 57740.60.18)
      /usr/local/opt/libgit2/lib/libgit2.1.0.dylib (compatibility version 1.0.0, current version 1.0.1)
      /usr/local/opt/openssl@1.1/lib/libssl.1.1.dylib (compatibility version 1.1.0, current version 1.1.0)
      /usr/local/opt/openssl@1.1/lib/libcrypto.1.1.dylib (compatibility version 1.1.0, current version 1.1.0)
      /usr/lib/libz.1.dylib (compatibility version 1.0.0, current version 1.2.8)
      /usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1238.60.2)
      /usr/lib/libresolv.9.dylib (compatibility version 1.0.0, current version 1.0.0)
    target/release/git-sugdiff.d: is not an object file

After:

    $ otool -L target/release/git-sug*
    target/release/git-sugapply:
      /System/Library/Frameworks/Security.framework/Versions/A/Security (compatibility version 1.0.0, current version 57740.60.18)
      /usr/lib/libiconv.2.dylib (compatibility version 7.0.0, current version 7.0.0)
      /System/Library/Frameworks/CoreFoundation.framework/Versions/A/CoreFoundation (compatibility version 150.0.0, current version 1349.8.0)
      /usr/lib/libz.1.dylib (compatibility version 1.0.0, current version 1.2.8)
      /usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1238.60.2)
      /usr/lib/libresolv.9.dylib (compatibility version 1.0.0, current version 1.0.0)
    target/release/git-sugapply.d: is not an object file
    target/release/git-sugdiff:
      /System/Library/Frameworks/Security.framework/Versions/A/Security (compatibility version 1.0.0, current version 57740.60.18)
      /usr/lib/libiconv.2.dylib (compatibility version 7.0.0, current version 7.0.0)
      /System/Library/Frameworks/CoreFoundation.framework/Versions/A/CoreFoundation (compatibility version 150.0.0, current version 1349.8.0)
      /usr/lib/libz.1.dylib (compatibility version 1.0.0, current version 1.2.8)
      /usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1238.60.2)
      /usr/lib/libresolv.9.dylib (compatibility version 1.0.0, current version 1.0.0)
    target/release/git-sugdiff.d: is not an object file

4 files changed, 28 insertions, 11 deletions

diff --git a/Cargo.lock b/Cargo.lock
index c9731da..eb593ca 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -258,9 +258,9 @@ dependencies = [
 
 [[package]]
 name = "git2"
-version = "0.13.8"
+version = "0.13.11"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e6ac22e49b7d886b6802c66662b12609452248b1bc9e87d6d83ecea3db96f557"
+checksum = "1e094214efbc7fdbbdee952147e493b00e99a4e52817492277e98967ae918165"
 dependencies = [
  "bitflags",
  "libc",
@@ -481,9 +481,9 @@ checksum = "a2f02823cf78b754822df5f7f268fb59822e7296276d3e069d8e8cb26a14bd10"
 
 [[package]]
 name = "libgit2-sys"
-version = "0.12.9+1.0.1"
+version = "0.12.13+1.0.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "9b33bf3d9d4c45b48ae1ea7c334be69994624dc0a69f833d5d9f7605f24b552b"
+checksum = "069eea34f76ec15f2822ccf78fe0cdb8c9016764d0a12865278585a74dbdeae5"
 dependencies = [
  "cc",
  "libc",
@@ -495,9 +495,9 @@ dependencies = [
 
 [[package]]
 name = "libssh2-sys"
-version = "0.2.18"
+version = "0.2.19"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "eafa907407504b0e683786d4aba47acf250f114d37357d56608333fd167dd0fc"
+checksum = "ca46220853ba1c512fc82826d0834d87b06bcd3c2a42241b7de72f3d2fe17056"
 dependencies = [
  "cc",
  "libc",
@@ -509,9 +509,9 @@ dependencies = [
 
 [[package]]
 name = "libz-sys"
-version = "1.0.25"
+version = "1.1.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "2eb5e43362e38e2bca2fd5f5134c4d4564a23a5c28e9b95411652021a8675ebe"
+checksum = "602113192b08db8f38796c4e85c39e960c145965140e918018bcde1952429655"
 dependencies = [
  "cc",
  "libc",
@@ -649,6 +649,15 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "77af24da69f9d9341038eba93a073b1fdaaa1b788221b00a69bce9e762cb32de"
 
 [[package]]
+name = "openssl-src"
+version = "111.10.2+1.1.1g"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a287fdb22e32b5b60624d4a5a7a02dbe82777f730ec0dbc42a0554326fef5a70"
+dependencies = [
+ "cc",
+]
+
+[[package]]
 name = "openssl-sys"
 version = "0.9.58"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -657,6 +666,7 @@ dependencies = [
  "autocfg",
  "cc",
  "libc",
+ "openssl-src",
  "pkg-config",
  "vcpkg",
 ]
diff --git a/Cargo.toml b/Cargo.toml
index 82632ee..e4ce989 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -6,7 +6,7 @@ edition = "2018"
 [dependencies]
 exitcode = "1.1.2"
 getopts = "0.2.21"
-git2 = "0.13.8"
+git2 = { version = "0.13.11", features = ["vendored-openssl"] }
 regex = "1.3.9"
 thiserror = "1.0.20"
 url = "2.1.1"
diff --git a/Makefile b/Makefile
index a0f8c73..7778be3 100644
--- a/Makefile
+++ b/Makefile
@@ -27,6 +27,13 @@ DIST := $(abspath dist)
 DIST_PRODUCTS := $(patsubst %,dist/%,$(PRODUCTS))
 DIST_MAN_PAGES := $(patsubst doc/%,dist/%,$(MAN_PAGES))
 
+# Set STATIC=1 to build a static binary.
+STATIC ?= 0
+
+ifeq ($(STATIC), 1)
+BUILD_VARS += PKG_CONFIG_LIBDIR=''
+endif
+
 
 .PHONY: doc
 doc: $(MAN_PAGES)
@@ -38,7 +45,7 @@ doc/%.1: doc/%.1.txt
 
 
 $(RELEASE_PRODUCTS): $(SOURCES)
-	cargo build --release
+	$(BUILD_VARS) cargo build --release
 
 
 .PHONY: dist
diff --git a/github-suggestion/Cargo.toml b/github-suggestion/Cargo.toml
index 34e197c..8962adc 100644
--- a/github-suggestion/Cargo.toml
+++ b/github-suggestion/Cargo.toml
@@ -4,7 +4,7 @@ version = "0.1.0"
 edition = "2018"
 
 [dependencies]
-git2 = "0.13.8"
+git2 = { version = "0.13.11", features = ["vendored-openssl"] }
 github-rs = "0.7.0"
 regex = "1.3.9"
 serde = { version = "1.0.114", features = ["derive"] }