'Returns [(path_to_gch, language_flag, language, header)].
|path_to_gch| and |header| are relative to the build directory.'

def GetPchBuildCommands(self, arch=None):

    if ((not self.header) or (not self.compile_headers)):
        return []
    return [(self._Gch('c', arch), '-x    c-header', 'c', self.header), (self._Gch('cc', arch), '-x    c++-header', 'cc', self.header), (self._Gch('m', arch), '-x    objective-c-header', 'm', self.header), (self._Gch('mm', arch), '-x    objective-c++-header', 'mm', self.header)]
