[MIPS] Use IRT shim instead of dummy IRT shim

IRT shim is needed as it whitelists NaCl IRT interfaces exposed under
PNaCl.

BUG= https://code.google.com/p/nativeclient/issues/detail?id=2275
TEST= Build Chromium for MIPS

Review URL: https://codereview.chromium.org/175533002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@252847 0039d316-1c4b-4281-b951-d872f2087c98
3 files changed