Move some constants from env to compiler constants

Library/Homebrew/compilers.rb

 module CompilerConstants
   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]|5)$/
+  COMPILER_SYMBOL_MAP = {
+    "gcc-4.0"  => :gcc_4_0,
+    "gcc-4.2"  => :gcc,
+    "llvm-gcc" => :llvm,
+    "clang"    => :clang,
+  }
+
+  COMPILERS = COMPILER_SYMBOL_MAP.values +
+    GNU_GCC_VERSIONS.map { |n| "gcc-#{n}" }
 end
 
 class CompilerFailure

Library/Homebrew/extend/ENV/shared.rb

@@ -7,16 +7,6 @@ module SharedEnvExtension
   CC_FLAG_VARS = %w{CFLAGS CXXFLAGS OBJCFLAGS OBJCXXFLAGS}
   FC_FLAG_VARS = %w{FCFLAGS FFLAGS}
 
-  COMPILER_SYMBOL_MAP = {
-    "gcc-4.0"  => :gcc_4_0,
-    "gcc-4.2"  => :gcc,
-    "llvm-gcc" => :llvm,
-    "clang"    => :clang,
-  }
-
-  COMPILERS = COMPILER_SYMBOL_MAP.values +
-    GNU_GCC_VERSIONS.map { |n| "gcc-#{n}" }
-
   SANITIZED_VARS = %w[
     CDPATH GREP_OPTIONS CLICOLOR_FORCE
     CPATH C_INCLUDE_PATH CPLUS_INCLUDE_PATH OBJC_INCLUDE_PATH