This patch implements .set mips32r2 directive and sets appropriate feature bits....

This patch implements .set mips32r2 directive and sets appropriate feature bits. It also introduces helper functions that are used to set and clear feature bits as necessary. This directive is a counterpart of -mips32r2 command line options with the exception that it does not influence elf header flags. The usage example is gives in test file.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@202807 91177308-0d34-0410-b5e6-96231b3b80d8