[mips] Add support to '.set mips64'.

The '.set mips64' directive enables the feature Mips:FeatureMips64
from assembly. Note that it doesn't modify the ELF header as opposed
to the use of -mips64 from the command-line. The reason for this
is that we want to be as compatible as possible with existing assemblers
like GAS.

llvm-svn: 204817
diff --git a/llvm/lib/Target/Mips/AsmParser/MipsAsmParser.cpp b/llvm/lib/Target/Mips/AsmParser/MipsAsmParser.cpp
index 2244e3d..35c1f4b 100644
--- a/llvm/lib/Target/Mips/AsmParser/MipsAsmParser.cpp
+++ b/llvm/lib/Target/Mips/AsmParser/MipsAsmParser.cpp
@@ -2489,6 +2489,10 @@
       setFeatureBits(Mips::FeatureMips32r2, "mips32r2");
       getTargetStreamer().emitDirectiveSetMips32R2();
     break;
+    case Mips::FeatureMips64:
+      setFeatureBits(Mips::FeatureMips64, "mips64");
+      getTargetStreamer().emitDirectiveSetMips64();
+    break;
     case Mips::FeatureMips64r2:
       setFeatureBits(Mips::FeatureMips64r2, "mips64r2");
       getTargetStreamer().emitDirectiveSetMips64R2();
@@ -2526,6 +2530,8 @@
       return parseSetFeature(Mips::FeatureMicroMips);
   } else if (Tok.getString() == "mips32r2") {
       return parseSetFeature(Mips::FeatureMips32r2);
+  } else if (Tok.getString() == "mips64") {
+      return parseSetFeature(Mips::FeatureMips64);
   } else if (Tok.getString() == "mips64r2") {
       return parseSetFeature(Mips::FeatureMips64r2);
   } else if (Tok.getString() == "dsp") {