Install: add BuildToolsError and BuildFlagsError

Add these new errors, and guards in formula installation and
cmd/{,un,re}install to match, move can_build? to the MacOS module,
flatten conditions, remove redundant can_build? check

reinstate removed (doctor) check

1 files changed, 13 insertions, 0 deletions

diff --git a/Library/Homebrew/extend/ARGV.rb b/Library/Homebrew/extend/ARGV.rb
index a8eb9a5d2..706b62568 100644
--- a/Library/Homebrew/extend/ARGV.rb
+++ b/Library/Homebrew/extend/ARGV.rb
@@ -200,6 +200,19 @@ module HomebrewArgvExtension
     value "env"
   end
 
+  # collect any supplied build flags into an array for reporting
+  def collect_build_flags
+    build_flags = []
+
+    build_flags << '--HEAD' if build_head?
+    build_flags << '--universal' if build_universal?
+    build_flags << '--32-bit' if build_32_bit?
+    build_flags << '--build-bottle' if build_bottle?
+    build_flags << '--build-from-source' if build_from_source?
+
+    build_flags
+  end
+
   private
 
   def spec(default = :stable)