gallivm: fix build with LLVM 18

Reviewed-by: Dave Airlie <airlied@redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/25388>

src/amd/llvm/ac_llvm_helper.cpp

@@ -250,7 +250,11 @@ struct ac_compiler_passes *ac_create_llvm_passes(LLVMTargetMachineRef tm)
    TargetMachine *TM = reinterpret_cast<TargetMachine *>(tm);
 
    if (TM->addPassesToEmitFile(p->passmgr, p->ostream, nullptr,
+#if LLVM_VERSION_MAJOR >= 18
+                               CodeGenFileType::ObjectFile)) {
+#else
                                CGFT_ObjectFile)) {
+#endif
       fprintf(stderr, "amd: TargetMachine can't emit a file of this type!\n");
       delete p;
       return NULL;