Add MIPS Technologies to the vendors in llvm::Triple.

This is a prerequisite for checking for 'mti' and 'img' in a consistent way in
clang. Previously 'img' could use Triple::getVendor() but 'mti' could only use
Triple::getVendorName().



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@213381 91177308-0d34-0410-b5e6-96231b3b80d8