Make sure GCMole pukes when Clang invocation fails.

tools/gcmole/gcmole.lua

 -- Copyright 2011 the V8 project authors. All rights reserved.
 -- Redistribution and use in source and binary forms, with or without
 -- modification, are permitted provided that the following conditions are
 -- met:
 --
 --     * Redistributions of source code must retain the above copyright
 --       notice, this list of conditions and the following disclaimer.
 --     * Redistributions in binary form must reproduce the above
 --       copyright notice, this list of conditions and the following
 --       disclaimer in the documentation and/or other materials provided
@@ skipping 99 matching lines @@
    local cmd_line = MakeClangCommandLine(cfg.plugin,
                                          cfg.plugin_args,
                                          cfg.triple,
                                          cfg.arch_define)
    for _, filename in ipairs(filenames) do
       log("-- %s", filename)
       local action = cmd_line .. " src/" .. filename .. " 2>&1"
       if FLAGS.verbose then print('popen ', action) end
       local pipe = io.popen(action)
       func(filename, pipe:lines())
-      pipe:close()
+      local success = pipe:close()
+      if not success then error("Failed to run: " .. action) end
    end
 end
 
 -------------------------------------------------------------------------------
 -- GYP file parsing
 
 local function ParseGYPFile()
    local f = assert(io.open("tools/gyp/v8.gyp"), "failed to open GYP file")
    local gyp = f:read('*a')
    f:close()
@@ skipping 240 matching lines @@
 
 for _, arch in ipairs(ARCHS) do
    if not ARCHITECTURES[arch] then
       error ("Unknown arch: " .. arch)
    end
 
    errors = SafeCheckCorrectnessForArch(arch, report) or errors
 end
 
 os.exit(errors and 1 or 0)