Fix a warning: default label in switch which covers all enumeration values (NFC)

Author: joker-eph

llvm/lib/Target/TargetMachineC.cpp

@@ -262,7 +262,7 @@ void LLVMSetTargetMachineGlobalISel(LLVMTargetMachineRef T, LLVMBool Enable) {
 
 void LLVMSetTargetMachineGlobalISelAbort(LLVMTargetMachineRef T,
                                          LLVMGlobalISelAbortMode Mode) {
-  GlobalISelAbortMode AM;
+  GlobalISelAbortMode AM = GlobalISelAbortMode::Enable;
   switch (Mode) {
   case LLVMGlobalISelAbortDisable:
     AM = GlobalISelAbortMode::Disable;
@@ -273,9 +273,6 @@ void LLVMSetTargetMachineGlobalISelAbort(LLVMTargetMachineRef T,
   case LLVMGlobalISelAbortDisableWithDiag:
     AM = GlobalISelAbortMode::DisableWithDiag;
     break;
-  default:
-    AM = GlobalISelAbortMode::Enable;
-    break;
   }
 
   unwrap(T)->setGlobalISelAbort(AM);