Re-commit r277988: [mips][ias] Fix all the hacks related to MIPS-specific unary opera...

Re-commit r277988: [mips][ias] Fix all the hacks related to MIPS-specific unary operators (%hi/%lo/%gp_rel/etc.).

Hopefully with the MSVC builds fixed. I've added a missing '#include <tuple>'
that gcc and clang don't seem to need.

llvm-svn: 277995