Fix MSVC "not all control paths return a value" warnings. NFC.

Author: RKSimon

clang/include/clang/Basic/TargetInfo.h

@@ -1386,7 +1386,7 @@ class TargetInfo : public TransferrableTargetInfo,
       case LangOptions::SignReturnAddressScopeKind::All:
         return "all";
       }
-      assert(false && "Unexpected SignReturnAddressScopeKind");
+      llvm_unreachable("Unexpected SignReturnAddressScopeKind");
     }
 
     const char *getSignKeyStr() const {
@@ -1396,7 +1396,7 @@ class TargetInfo : public TransferrableTargetInfo,
       case LangOptions::SignReturnAddressKeyKind::BKey:
         return "b_key";
       }
-      assert(false && "Unexpected SignReturnAddressKeyKind");
+      llvm_unreachable("Unexpected SignReturnAddressKeyKind");
     }
   };