Use Xcode's clang instead of Homebrew's clang

The new Xcode update breaks Homebrew's clang. See #40

BUILDING.md

@@ -92,10 +92,9 @@ Credits to [9Morello](//github.com/9Morello) for most of the work done on this p
 ### Setting up the build environment
 
 1. Setup [Homebrew Versions](//github.com/Homebrew/homebrew-versions) if you haven't already: `brew tap homebrew/versions`
-2. Install LLVM 3.8 via Homebrew: `brew install llvm38 --with-clang --with-clang-extra-tools`
-3. Install GCC 4.9 via Homebrew: `brew install gcc49`
-4. Install GNU patch via Homebrew: `brew install homebrew/dupes/gpatch`
-5. Install Quilt via Homebrew: `brew install quilt`
+2. Install GCC 4.9 via Homebrew: `brew install gcc49`
+3. Install GNU patch via Homebrew: `brew install homebrew/dupes/gpatch`
+4. Install Quilt via Homebrew: `brew install quilt`
 5. Try running `svn info https://llvm.org/svn/llvm-project`
     * If asked to verify llvm.org's certificate fingerprint, accept it permanently and run this command again
         * If still asked to accept the fingerprint, try the solutions [on this page](http://stackoverflow.com/questions/6115170/svn-error-validating-server-certificate). Then try rerunning the command to verify the certificate is accepted.

buildlib/macos.py

@@ -69,8 +69,6 @@ def check_build_environment(self):
 
         self.logger.info("Checking compilers...")
         compiler_list = [ # TODO: Move these paths to another config file?
-            "/usr/local/Cellar/llvm/3.8.1/bin/clang",
-            "/usr/local/Cellar/llvm/3.8.1/bin/clang++",
             "/usr/local/Cellar/gcc49/4.9.3/bin/x86_64-apple-darwin15.4.0-c++-4.9"]
         for compiler in compiler_list:
             if not pathlib.Path(compiler).is_file():

resources/macos/gyp_flags

@@ -1,8 +1,3 @@
 clang=1
 clang_use_chrome_plugins=0
-clang_dir=/usr/local/Cellar/llvm/3.8.1/bin
-make_clang_dir=/usr/local/Cellar/llvm/3.8.1
-host_cc=/usr/local/Cellar/llvm/3.8.1/bin/clang
-CC=/usr/local/Cellar/llvm/3.8.1/bin/clang
-host_cxx=/usr/local/Cellar/llvm/3.8.1/bin/clang++
-LDPLUSPLUS=/usr/local/Cellar/llvm/3.8.1/bin/clang++
+clang_xcode=1