compilers: support gcc 5

Closes Homebrew/homebrew#39470.

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

Library/ENV/4.3/g++-5

@@ -0,0 +1 @@
+cc

Library/ENV/4.3/gcc-5

@@ -0,0 +1 @@
+cc

Library/Homebrew/compilers.rb

@@ -1,6 +1,6 @@
 module CompilerConstants
-  GNU_GCC_VERSIONS = 3..9
+  GNU_GCC_VERSIONS = %w[4.3 4.4 4.5 4.6 4.7 4.8 4.9 5]
-  GNU_GCC_REGEXP = /^gcc-(4\.[3-9])$/
+  GNU_GCC_REGEXP = /^gcc-(4\.[3-9]|5)$/
 end
 
 class CompilerFailure
@@ -107,7 +107,7 @@ class CompilerSelector
       case compiler
       when :gnu
         GNU_GCC_VERSIONS.reverse_each do |v|
-          name = "gcc-4.#{v}"
+          name = "gcc-#{v}"
           version = compiler_version(name)
           yield Compiler.new(name, version) if version
         end

Library/Homebrew/extend/ENV/shared.rb

@@ -15,7 +15,7 @@ module SharedEnvExtension
   }
 
   COMPILERS = COMPILER_SYMBOL_MAP.values +
-    GNU_GCC_VERSIONS.map { |n| "gcc-4.#{n}" }
+    GNU_GCC_VERSIONS.map { |n| "gcc-#{n}" }
 
   SANITIZED_VARS = %w[
     CDPATH GREP_OPTIONS CLICOLOR_FORCE

Library/Homebrew/extend/ENV/std.rb

@@ -130,7 +130,7 @@ module Stdenv
   alias_method :gcc_4_2, :gcc
 
   GNU_GCC_VERSIONS.each do |n|
-    define_method(:"gcc-4.#{n}") do
+    define_method(:"gcc-#{n}") do
       super()
       set_cpu_cflags
     end