Implement fails_with for non-Apple compilers

This adds support for non-Apple GCC compilers in the fails_with code.
A fails_with block for a non-Apple compiler looks like:

fails_with :gcc => '4.8.1' do
  cause 'Foo'
end

Non-Apple compilers don't have build numbers, so compiler failures are
based on version strings instead.

Internally non-Apple compilers can be distinguished because they are
passed around as strings instead of symbols.

In addition, this alters the priority list for compilers, with the
following changes:

* Apple GCC 4.2 and LLVM-GCC swap positions, with GCC now taking
  priority. (Maybe LLVM-GCC should just go away.)
* Non-Apple GCC compilers are ranked below GCC 4.2 but above LLVM-GCC
  and Apple GCC 4.0.

1 files changed, 10 insertions, 0 deletions

diff --git a/Library/Homebrew/macos.rb b/Library/Homebrew/macos.rb
index 8e379ad2a..de109ade3 100644
--- a/Library/Homebrew/macos.rb
+++ b/Library/Homebrew/macos.rb
@@ -151,6 +151,16 @@ module MacOS extend self
       end
   end
 
+  def non_apple_gcc_version(cc)
+    return unless path = locate(cc)
+
+    ivar = "@#{cc.gsub(/(-|\.)/, '')}_version"
+    return instance_variable_get(ivar) if instance_variable_defined?(ivar)
+
+    `#{path} --version` =~ /gcc-\d.\d \(GCC\) (\d\.\d\.\d)/
+    instance_variable_set(ivar, $1)
+  end
+
   # See these issues for some history:
   # http://github.com/mxcl/homebrew/issues/#issue/13
   # http://github.com/mxcl/homebrew/issues/#issue/41