[mips] Use __clear_cache builtin instead of cacheflush() in Unix...

[mips] Use __clear_cache builtin instead of cacheflush() in Unix Memory::InvalidateInstructionCache()

MIPS64 Android bionic has removed cacheflush(). Use __clear_cache() instead for 32-bit and 64-bit MIPS

Patch by Duane Sand <Duane.Sand@imgtec.com>

llvm-svn: 211588