[SYCL][RTC] Fix warning caused by default case (#16243)

Fix warning resulting from default case covering other cases, causing
post-commit to fail.

---------

Signed-off-by: Lukas Sommer <[email protected]>

Author: sommerlukas

sycl-jit/jit-compiler/lib/rtc/DeviceCompilation.cpp

@@ -202,15 +202,11 @@ class LLVMDiagnosticWrapper : public llvm::DiagnosticHandler {
     auto Prefix = [](DiagnosticSeverity Severity) -> llvm::StringLiteral {
       switch (Severity) {
       case llvm::DiagnosticSeverity::DS_Error:
-        return "ERROR";
+        return "ERROR:";
       case llvm::DiagnosticSeverity::DS_Warning:
-        return "WARNING";
-      case llvm::DiagnosticSeverity::DS_Note:
-        return "NOTE:";
-      case llvm::DiagnosticSeverity::DS_Remark:
-        return "REMARK:";
+        return "WARNING:";
       default:
-        llvm_unreachable("Unhandled case");
+        return "NOTE:";
       }
     }(DI.getSeverity());
     LogPrinter << Prefix;