[llvm] [X86Backend] Use GetExternalSymbolSymbol for MO_ExternalSymbol. (PR #133352)

[weiwei chen via llvm-commits]

================
@@ -0,0 +1,173 @@
+//===- llvm/unittest/CodeGen/X86MCInstLowerTest.cpp
+//-------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "TestAsmPrinter.h"
+#include "llvm/AsmParser/Parser.h"
+#include "llvm/CodeGen/AsmPrinter.h"
+#include "llvm/CodeGen/MachineModuleInfo.h"
+#include "llvm/CodeGen/TargetLowering.h"
+#include "llvm/CodeGen/TargetPassConfig.h"
+#include "llvm/IR/LegacyPassManager.h"
+#include "llvm/IR/MDBuilder.h"
+#include "llvm/IR/Module.h"
+#include "llvm/MC/MCStreamer.h"
+#include "llvm/MC/TargetRegistry.h"
+#include "llvm/Support/SourceMgr.h"
+#include "llvm/Support/TargetSelect.h"
+#include "llvm/Target/TargetLoweringObjectFile.h"
+#include "llvm/Target/TargetMachine.h"
+#include "gtest/gtest.h"
+
+namespace llvm {
+
+class X86MCInstLowerTest : public testing::Test {
+protected:
+  static void SetUpTestCase() {
+    LLVMInitializeX86TargetInfo();
----------------
weiweichen wrote:

Looks like compilation will fail if I'm not building X86 backend. Changing this to 
```
    InitializeAllTargetMCs();
    InitializeAllTargetInfos();
    InitializeAllTargets();
    InitializeAllAsmPrinters();
```

Tested with only building AArch64 backend, this test gets skipped.

```
[==========] Running 1 test from 1 test suite.
[----------] Global test environment set-up.
[----------] 1 test from X86MCInstLowerTest
[ RUN      ] X86MCInstLowerTest.moExternalSymbol_MCSYMBOL
/Users/weiwei.chen/research/modularml/modular/third-party/llvm-project/llvm/unittests/CodeGen/X86MCInstLowerTest.cpp:107: Skipped


[  SKIPPED ] X86MCInstLowerTest.moExternalSymbol_MCSYMBOL (1 ms)
[----------] 1 test from X86MCInstLowerTest (1 ms total)

[----------] Global test environment tear-down
[==========] 1 test from 1 test suite ran. (2 ms total)
[  PASSED  ] 0 tests.
[  SKIPPED ] 1 test, listed below:
[  SKIPPED ] X86MCInstLowerTest.moExternalSymbol_MCSYMBOL
```

https://github.com/llvm/llvm-project/pull/133352