Added --use-gcc flag.

This allows you to use llvm as your default compiler and keep the cc symlink
pointed at llvm, while allowing you to build forumla that requires the gcc.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>

Library/Contributions/manpages/brew.1.md

@@ -275,6 +275,10 @@ Some sample commands ship with Homebrew and are enabled by default.
     This issue typically occurs when using FileVault or custom SSD
     configurations.
 
+  * HOMEBREW\_USE\_GCC:
+    If set, instructs Homebrew to use gcc, even if the system default
+    is currently set to LLVM.
+
   * HOMEBREW\_USE\_LLVM:
     If set, instructs Homebrew to use the LLVM front-ends to the GCC
     compilers.

Library/Homebrew/cmd/--env.rb

@@ -10,6 +10,7 @@ def __env
 
   def dump_build_env env
     puts %["--use-llvm" was specified] if ARGV.include? '--use-llvm'
+    puts "\"--use-gcc\" was specified" if ARGV.include? '--use-gcc'
 
     %w[ CC CXX LD ].each do |k|
       value = env[k]
@@ -24,7 +25,7 @@ def dump_build_env env
     end
 
     %w[ CFLAGS CXXFLAGS CPPFLAGS LDFLAGS MACOSX_DEPLOYMENT_TARGET MAKEFLAGS PKG_CONFIG_PATH
-        HOMEBREW_DEBUG HOMEBREW_VERBOSE HOMEBREW_USE_LLVM HOMEBREW_SVN ].each do |k|
+        HOMEBREW_DEBUG HOMEBREW_VERBOSE HOMEBREW_USE_GCC HOMEBREW_USE_LLVM HOMEBREW_SVN ].each do |k|
       value = env[k]
       puts "#{k}: #{value}" if value
     end

Library/Homebrew/cmd/doctor.rb

@@ -147,6 +147,9 @@ def check_cc_symlink
         To force Homebrew to use LLVM, you can set the "HOMEBREW_LLVM" environmental
         variable, or pass "--use-llvm" to "brew install".
 
+        To force Homebrew to use gcc, you can set the "HOMEBREW_GCC" environmental
+        variable, or pass "--use-gcc" to "brew install".
+
       EOS
     end
 end

Library/Homebrew/extend/ENV.rb

@@ -24,6 +24,10 @@ def setup_build_environment
       self['CC'] = "#{xcode_path}/usr/bin/llvm-gcc"
       self['CXX'] = "#{xcode_path}/usr/bin/llvm-g++"
       cflags = ['-O4'] # link time optimisation baby!
+    elsif MACOS_VERSION >= 10.6 and (self['HOMEBREW_USE_GCC'] or ARGV.include? '--use-gcc')
+      self['CC'] = '/usr/bin/gcc'
+      self['CXX'] = '/usr/bin/g++'
+      cflags = ['-O3']
     else
       # If these aren't set, many formulae fail to build
       self['CC'] = '/usr/bin/cc'

share/man/man1/brew.1

@@ -298,6 +298,10 @@ If set, instructs Homebrew to use \fBHOMEBREW_TEMP\fR as the temporary folder fo
 This issue typically occurs when using FileVault or custom SSD configurations\.
 .
 .TP
+HOMEBREW_USE_GCC
+If set, instructs Homebrew to use gcc, even if the system default is currently set to LLVM\.
+.
+.TP
 HOMEBREW_USE_LLVM
 If set, instructs Homebrew to use the LLVM front\-ends to the GCC compilers\.
 .