Apply local patches when building llvm on Mac.

[sas]

Summary

This is already done when building for linux with the CMake build
system. This functionality disappeared recently when some of the build
scripts used by the xcode build system changed.

scripts/Xcode/build-llvm.py

 #!/usr/bin/env python
 
 import errno
 import hashlib
+import fnmatch
 import os
 import platform
 import subprocess
 import sys
 
 from lldbbuild import *
 
 #### SETTINGS ####
def md5 (string):
     m.update(string)
     return m.hexdigest()
 
 def all_source_control_status_md5 ():
     return md5(all_source_control_status())
 
 #### CHECKING OUT AND BUILDING LLVM ####
 
+def apply_patches(spec):
+    files = os.listdir(os.path.join(lldb_source_path(), 'scripts'))
+    patches = [f for f in files if fnmatch.fnmatch(f, spec['name'] + '.*.diff')]
+    for p in patches:
+        run_in_directory(["patch", "-p0", "-i", os.path.join(lldb_source_path(), 'scripts', p)], spec['root'])
+
 def check_out_if_needed(spec):
     if not os.path.isdir(spec['root']):
         vcs(spec).check_out()
+        apply_patches(spec)
 
 def all_check_out_if_needed ():
     map (check_out_if_needed, XCODE_REPOSITORIES())
 
 def should_build_llvm ():
     if build_type() == BuildType.Xcode:
         # TODO use md5 sums
         return True