superenv: find Homebrew's gcc-4.2

If we're using a homebrewed gcc-4.2, xcrun may fail to find it (or,
worse, find superenv's shim instead). Explicitly add it to the PATH and
search all path elements for the requested tool.

Also make sure to specify 'gcc-4.2' as the compiler name, not plain
'gcc'. That can resolve to llvm-gcc and to gcc-4.0 on various Xcodes.

Library/ENV/4.3/xcrun

@@ -21,7 +21,11 @@ try `/usr/bin/xcrun --find #{arg0}`.chomp
 # Nuts, Xcode is not setup properly or something. Try to find the tools anyway!
 try "#{ENV['DEVELOPER_DIR']}/usr/bin/#{arg0}"
 try "#{ENV['DEVELOPER_DIR']}/Toolchains/XcodeDefault.xctoolchain/usr/bin/#{arg0}"
-try "/usr/bin/#{arg0}"
+# xcrun won't always be able to find Homebrew's apple-gcc42,
+# even when it's in the PATH
+ENV['PATH'].split(':').each do |p|
+  try "#{p}/#{arg0}"
+end
 
 abort <<-EOS
 Your Xcode and or CLT are mis-configured. Try some or all of the following:

Library/Homebrew/superenv.rb

@@ -61,6 +61,13 @@ class << ENV
     ENV['CMAKE_INCLUDE_PATH'] = determine_cmake_include_path
     ENV['CMAKE_LIBRARY_PATH'] = determine_cmake_library_path
     ENV['ACLOCAL_PATH'] = determine_aclocal_path
+
+    # Homebrew's apple-gcc42 will be outside the PATH in superenv,
+    # so xcrun may not be able to find it
+    if ENV['HOMEBREW_CC'] == 'gcc-4.2' && !MacOS.locate('gcc-4.2')
+      apple_gcc42 = Formula.factory('apple-gcc42') rescue nil
+      ENV.append('PATH', apple_gcc42.opt_prefix/'bin', ':') if apple_gcc42
+    end
   end
 
   def universal_binary
@@ -76,8 +83,13 @@ class << ENV
 
   def determine_cc
     if ARGV.include? '--use-gcc'
+      gcc_installed = Formula.factory('apple-gcc42').installed? rescue false
       # fall back to something else on systems without Apple gcc
-      MacOS.locate('gcc-4.2') ? "gcc-4.2" : raise("gcc-4.2 not found!")
+      if MacOS.locate('gcc-4.2') || gcc_installed
+        "gcc-4.2"
+      else
+        raise("gcc-4.2 not found!")
+      end
     elsif ARGV.include? '--use-llvm'
       "llvm-gcc"
     elsif ARGV.include? '--use-clang'
@@ -93,7 +105,10 @@ class << ENV
       "gcc"
     elsif ENV['HOMEBREW_CC']
       case ENV['HOMEBREW_CC']
-        when 'clang', 'gcc', 'gcc-4.0' then ENV['HOMEBREW_CC']
+        when 'clang', 'gcc-4.0' then ENV['HOMEBREW_CC']
+        # depending on Xcode version plain 'gcc' could actually be
+        # gcc-4.0 or llvm-gcc
+        when 'gcc' then 'gcc-4.2'
         when 'llvm', 'llvm-gcc' then 'llvm-gcc'
       else
         opoo "Invalid value for HOMEBREW_CC: #{ENV['HOMEBREW_CC']}"
@@ -106,7 +121,7 @@ class << ENV
     case MacOS.default_compiler
     when :clang   then 'clang'
     when :llvm    then 'llvm-gcc'
-    when :gcc     then 'gcc'
+    when :gcc     then 'gcc-4.2'
     when :gcc_4_0 then 'gcc-4.0'
     end
   end