Remove dead code. Improve llvm_unreachable text. Simplify some control flow.

llvm-svn: 150918
diff --git a/llvm/lib/Target/Mips/MipsAsmPrinter.cpp b/llvm/lib/Target/Mips/MipsAsmPrinter.cpp
index fbc5f7d..9ddc08a 100644
--- a/llvm/lib/Target/Mips/MipsAsmPrinter.cpp
+++ b/llvm/lib/Target/Mips/MipsAsmPrinter.cpp
@@ -246,11 +246,8 @@
   case MipsSubtarget::N32:  return "abiN32";
   case MipsSubtarget::N64:  return "abi64";
   case MipsSubtarget::EABI: return "eabi32"; // TODO: handle eabi64
-  default: break;
+  default: llvm_unreachable("Unknown Mips ABI");;
   }
-
-  llvm_unreachable("Unknown Mips ABI");
-  return NULL;
 }
 
 void MipsAsmPrinter::EmitFunctionEntryLabel() {