Have CMake LLVM build share CFLAGS/CXXFLAGS with autoconf (e.g., libc++ flags).

toolchain_build/command.py

 #!/usr/bin/python
 # Copyright (c) 2012 The Native Client Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """Class capturing a command invocation as data."""
 
 import inspect
 import glob
 import hashlib
@@ skipping 178 matching lines @@
     cwd = subst.SubstituteAbsPaths(check_call_kwargs.get('cwd', '.'))
     subst.SetCwd(cwd)
     check_call_kwargs['cwd'] = cwd
 
     # Extract paths from kwargs and add to the command environment.
     path_dirs = []
     if 'path_dirs' in check_call_kwargs:
       path_dirs = [subst.Substitute(dirname) for dirname
                    in check_call_kwargs['path_dirs']]
       del check_call_kwargs['path_dirs']
-    check_call_kwargs['env'] = PlatformEnvironment(path_dirs)
+    # Perform substitution on any env overrides.
+    if 'env' in check_call_kwargs:
+      check_call_kwargs['env'] = { k: subst.Substitute(v)
+            for (k, v) in check_call_kwargs['env'].iteritems() }
+      check_call_kwargs['env'].update(PlatformEnvironment(path_dirs))
+    else:
+      check_call_kwargs['env'] = PlatformEnvironment(path_dirs)
 
     if isinstance(command, str):
       command = subst.Substitute(command)
     else:
       command = [subst.Substitute(arg) for arg in command]
       paths = check_call_kwargs['env']['PATH'].split(os.pathsep)
       command[0] = pynacl.file_tools.Which(command[0], paths=paths)
 
     if stdout is not None:
       stdout = subst.SubstituteAbsPaths(stdout)
@@ skipping 378 matching lines @@
 # It describes how to unpack and apply patches to produce the source
 # tree of the %(name)s component of a toolchain targetting Native Client.
 
 # Source: %(upstream-name)s.tar
 """
               % info)
       for patch in patch_files:
         f.write('\n# %s\n%s\n' % patch)
 
   return Runnable(run_cond, generatePatches, git_dir, info)