Reverting r237234, "Use std::bitset for SubtargetFeatures"

The buildbots are still not satisfied.
MIPS and ARM are failing (even though at least MIPS was expected to pass).

llvm-svn: 237245
diff --git a/llvm/lib/Target/Mips/MCTargetDesc/MipsMCCodeEmitter.cpp b/llvm/lib/Target/Mips/MCTargetDesc/MipsMCCodeEmitter.cpp
index 256cdfd..0cb8d55 100644
--- a/llvm/lib/Target/Mips/MCTargetDesc/MipsMCCodeEmitter.cpp
+++ b/llvm/lib/Target/Mips/MCTargetDesc/MipsMCCodeEmitter.cpp
@@ -112,11 +112,11 @@
 }
 
 bool MipsMCCodeEmitter::isMicroMips(const MCSubtargetInfo &STI) const {
-  return STI.getFeatureBits()[Mips::FeatureMicroMips];
+  return STI.getFeatureBits() & Mips::FeatureMicroMips;
 }
 
 bool MipsMCCodeEmitter::isMips32r6(const MCSubtargetInfo &STI) const {
-  return STI.getFeatureBits()[Mips::FeatureMips32r6];
+  return STI.getFeatureBits() & Mips::FeatureMips32r6;
 }
 
 void MipsMCCodeEmitter::EmitByte(unsigned char C, raw_ostream &OS) const {