[CIR][NFC] Improve the output for missing builtin calls (#163884)

This improves the diagnostic emitted when `errorNYI` is called for missing builtin calls so that the builtin being called is displayed in the diagnostic.

Author: andykaylor

clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp

@@ -463,7 +463,9 @@ RValue CIRGenFunction::emitBuiltinExpr(const GlobalDecl &gd, unsigned builtinID,
  return emitLibraryCall(*this, fd, e,
  cgm.getBuiltinLibFunction(fd, builtinID));
 
- cgm.errorNYI(e->getSourceRange(), "unimplemented builtin call");
+ cgm.errorNYI(e->getSourceRange(),
+ std::string("unimplemented builtin call: ") +
+ getContext().BuiltinInfo.getName(builtinID));
  return getUndefRValue(e->getType());
 }