[clang] Prefer clang_setup over use_clang

This patch switches over uses of use_clang to clang_setup to fix a
potential race condition that has been impacting CI.

This is split from the refactoring to ensure I'm not missing anything
major here on the clang-tools-extra side.

This should fix #145703.

Reviewers: AaronBallman, HighCommander4, HerrCai0907, petrhosek, Keenuts

Reviewed By: petrhosek

Pull Request: https://github.com/llvm/llvm-project/pull/147437

clang-tools-extra/clangd/test/lit.cfg.py

@@ -1,7 +1,7 @@
 import lit.llvm
 
 lit.llvm.initialize(lit_config, config)
-lit.llvm.llvm_config.use_clang([], [], required=False)
+lit.llvm.llvm_config.clang_setup()
 lit.llvm.llvm_config.use_default_substitutions()
 
 config.name = "Clangd"

clang-tools-extra/test/lit.cfg.py

@@ -42,7 +42,7 @@ config.test_source_root = os.path.dirname(__file__)
 config.test_exec_root = os.path.join(config.clang_tools_binary_dir, "test")
 
 # Tools need the same environment setup as clang (we don't need clang itself).
-llvm_config.use_clang(required=False)
+llvm_config.clang_setup()
 
 if config.clang_tidy_staticanalyzer:
     config.available_features.add("static-analyzer")