Default compiler is gcc on Linux

Library/Homebrew/compilers.rb

@@ -3,6 +3,7 @@ module CompilerConstants
   GNU_GCC_VERSIONS = %w[4.3 4.4 4.5 4.6 4.7 4.8 4.9 5 6 7 8].freeze
   GNU_GCC_REGEXP = /^gcc-(4\.[3-9]|[5-8])$/
   COMPILER_SYMBOL_MAP = {
+    "gcc"        => :gcc,
     "gcc-4.0"    => :gcc_4_0,
     "gcc-4.2"    => :gcc_4_2,
     "clang"      => :clang,
@@ -101,6 +102,7 @@ class CompilerSelector
     clang: [:clang, :gcc_4_2, :gnu, :gcc_4_0, :llvm_clang],
     gcc_4_2: [:gcc_4_2, :gnu, :clang, :gcc_4_0],
     gcc_4_0: [:gcc_4_0, :gcc_4_2, :gnu, :clang],
+    gcc: [:gnu, :gcc, :llvm_clang, :clang, :gcc_4_2, :gcc_4_0],
   }.freeze
 
   def self.select_for(formula, compilers = self.compilers)
@@ -150,9 +152,9 @@ class CompilerSelector
   end
 
   def compiler_version(name)
-    case name
-    when GNU_GCC_REGEXP
-      versions.non_apple_gcc_version(name)
+    case name.to_s
+    when "gcc", GNU_GCC_REGEXP
+      versions.non_apple_gcc_version(name.to_s)
     else
       versions.send("#{name}_build_version")
     end

Library/Homebrew/development_tools.rb

@@ -99,7 +99,7 @@ class DevelopmentTools
         path = HOMEBREW_PREFIX/"opt/gcc/bin"/cc
         path = locate(cc) unless path.exist?
         version = if path &&
-                     build_version = `#{path} --version`[/gcc(?:-\d(?:\.\d)? \(.+\))? (\d\.\d\.\d)/, 1]
+                     build_version = `#{path} --version`[/gcc(?:(?:-\d(?:\.\d)?)? \(.+\))? (\d\.\d\.\d)/, 1]
           Version.new build_version
         else
           Version::NULL

Library/Homebrew/extend/ENV/shared.rb

@@ -319,7 +319,11 @@ module SharedEnvExtension
   def compiler_with_cxx11_support?(cc)
     return if compiler_any_clang?(cc)
 
-    version = cc[/^gcc-(\d+(?:\.\d+)?)$/, 1]
+    version = if cc == :gcc
+      non_apple_gcc_version "gcc"
+    else
+      cc[/^gcc-(\d+(?:\.\d+)?)$/, 1]
+    end
     version && Version.create(version) >= Version.create("4.8")
   end
 

Library/Homebrew/extend/os/development_tools.rb

@@ -1 +1,5 @@
-require "extend/os/mac/development_tools" if OS.mac?
+if OS.mac?
+  require "extend/os/mac/development_tools"
+elsif OS.linux?
+  require "extend/os/linux/development_tools"
+end

Library/Homebrew/extend/os/linux/development_tools.rb

@@ -0,0 +1,7 @@
+class DevelopmentTools
+  class << self
+    def default_compiler
+      :gcc
+    end
+  end
+end