Fix test runner to properly emulate mm/mmm.

Really weird errors get thrown with absolute paths for
`ONE_SHOT_MAKEFILE` now.

Change-Id: I10a86dfd2dab43f03bcd3ce9a8c2551decd65bc4

test/libcxx/android/test/config.py

@@ -40,7 +40,7 @@ class Configuration(libcxx.test.config.Configuration):
 
     def configure_build_cmds(self):
         os.chdir(self.config.android_root)
-        self.build_cmds_dir = os.path.join(self.libcxx_src_root, 'buildcmds')
+        self.build_cmds_dir = 'external/libcxx/buildcmds'
         if not libcxx.android.build.mm(self.build_cmds_dir,
                                        self.config.android_root):
             raise RuntimeError('Could not generate build commands.')