Convert some assert(0) to llvm_unreachable or fold an 'if' condition into the assert.

llvm-svn: 211254
diff --git a/llvm/lib/Target/ARM/MCTargetDesc/ARMMCCodeEmitter.cpp b/llvm/lib/Target/ARM/MCTargetDesc/ARMMCCodeEmitter.cpp
index 5b51a52..b8ee555 100644
--- a/llvm/lib/Target/ARM/MCTargetDesc/ARMMCCodeEmitter.cpp
+++ b/llvm/lib/Target/ARM/MCTargetDesc/ARMMCCodeEmitter.cpp
@@ -1047,8 +1047,7 @@
   // we have a movt or a movw, but that led to misleadingly results.
   // This is now disallowed in the the AsmParser in validateInstruction()
   // so this should never happen.
-  assert(0 && "expression without :upper16: or :lower16:");
-  return 0;
+  llvm_unreachable("expression without :upper16: or :lower16:");
 }
 
 uint32_t ARMMCCodeEmitter::