[clang] Register all LLVM targets in AllClangUnitTest main

Addresses feedback in llvm#134196 (comment)

Makes the tests less sensitive to target registration from unrelated
test fixtures by registering everything up front.

Author: rnk

clang/unittests/AllClangUnitTests.cpp

@@ -0,0 +1,24 @@
+//===- clang/unittests/AllClangUnitTests.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 "gtest/gtest.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/TargetSelect.h"
+
+// This custom main entry point for the AllClangUnitTests binary registers all
+// tests on startup, so the tests don't become sensitive to target registration
+// within the test suite.
+int main(int argc, char **argv) {
+  ::testing::InitGoogleTest(&argc, argv);
+  llvm::cl::ParseCommandLineOptions(argc, argv);
+
+  llvm::InitializeAllTargets();
+  llvm::InitializeAllTargetMCs();
+
+  return RUN_ALL_TESTS();
+}

clang/unittests/CMakeLists.txt

@@ -117,6 +117,7 @@ get_property(LINK_LIBS GLOBAL PROPERTY CLANG_UNITTEST_LINK_LIBS)
 get_property(LLVM_COMPONENTS GLOBAL PROPERTY CLANG_UNITTEST_LLVM_COMPONENTS)
 add_distinct_clang_unittest(AllClangUnitTests
   ${SRCS}
+  AllClangUnitTests.cpp
   CLANG_LIBS
   ${CLANG_LIBS}
   LINK_LIBS