Xcode-only: Clean up compiler flags. Use CPATH.

- When using CPATH, we only need -isysroot and not the other -I spam.
- LDFLAGS use -isysroot instead of -L
  Turns out that the linker also understands the
  -isysroot flag which behaves more natural (in the
  sense: "like the internal defaults `/usr/lib` etc.)
  than adding `-L$(SDKROOT).
  Especially for duplicates, the linker first searches
  through all `-L` dirs and then looks at the sysroot
  or internal defaults. This is what we want.
- Pkg-config needs CC with CFLAGS passed to configure.

Closes #14351.

Signed-off-by: Jack Nagel <jacknagel@gmail.com>

1 files changed, 11 insertions, 4 deletions

diff --git a/Library/Formula/pkg-config.rb b/Library/Formula/pkg-config.rb
index 5449007c0..8e47b2b00 100644
--- a/Library/Formula/pkg-config.rb
+++ b/Library/Formula/pkg-config.rb
@@ -21,10 +21,17 @@ class PkgConfig < Formula
         /usr/local/lib/pkgconfig
         /usr/lib/pkgconfig
       ].uniq
-    system "./configure", "--disable-debug",
-                          "--prefix=#{prefix}",
-                          "--with-pc-path=#{paths*':'}",
-                          "--with-internal-glib"
+
+    args = %W[
+        --disable-debug
+        --prefix=#{prefix}
+        --with-pc-path=#{paths*':'}
+        --with-internal-glib
+      ]
+    args << "CC=#{ENV.cc} #{ENV.cflags}" unless MacOS::CLT.installed?
+
+    system "./configure", *args
+
     system "make"
     system "make check"
     system "make install"