[Mips] Add tests to check MIPS arch macros.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@200221 91177308-0d34-0410-b5e6-96231b3b80d8
[Mips] Change default CPU for MIPS 32/64 targets. Now they are mips32r2/mips64r2 respectively.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@200222 91177308-0d34-0410-b5e6-96231b3b80d8
[Mips] Fix __mips macro definition.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@200223 91177308-0d34-0410-b5e6-96231b3b80d8