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
diff --git a/llvm/lib/Target/Mips/MCTargetDesc/MipsMCAsmInfo.cpp b/llvm/lib/Target/Mips/MCTargetDesc/MipsMCAsmInfo.cpp
index 1ce8f07..2c01f91 100644
--- a/llvm/lib/Target/Mips/MCTargetDesc/MipsMCAsmInfo.cpp
+++ b/llvm/lib/Target/Mips/MCTargetDesc/MipsMCAsmInfo.cpp
@@ -49,6 +49,7 @@
   SupportsDebugInformation = true;
   ExceptionsType = ExceptionHandling::DwarfCFI;
   DwarfRegNumForCFI = true;
+  HasMipsExpressions = true;
 
   // Enable IAS by default for O32.
   if (TheTriple.getArch() == Triple::mips ||