Preprocessor/mmx.c and Preprocessor/predefined-arch-macros.c failed on MIPS

Separated from "[PATCH] Fix clang test failures on MIPS" thread.

Clang :: Preprocessor/mmx.c
Clang :: Preprocessor/predefined-arch-macros.c

These test check definitions of various i386..x86-64 platforms specific
macros. I suggest to add "mips" to the XFAIL list for these tests.

For those two tests, could you just force an appropriate triple with

Yes, it is possible. The appropriate patch "tgt-force.patch" is
attached to this mail. But I'm not absolutely sure that this approach
is correct. If we pass a target triple explicitly, we check predefined
macros on that target only. If we do not pass a target triple, we
check predefined macros on each different target where we run the test
suite and we cover more cases.

But if you do not see any problem here and "tgt-force.patch" is okay,
I will commit it.

tgt-force.patch (24.3 KB)

The benefit from the extra testing would be slight... better to just
make it consistent. Patch is fine.



Specifically, if we believe there might be differences from target to target, we should add explicit runs with those triples so that developers on other targets get the testing too…

Thanks for review. Committed at r156500.