[cross-project-tests] Make clang optional if not in LLVM_ENABLE_PROJECTS - part 4

[jhenderson]

Summary

Also mark debuginfo_tests as UNSUPPORTED if clang can't be found and remove it from the list of test dependencies if not in LLVM_ENABLE_PROJECTS.

Depends on D96510.

[aprantl]

This makes sense to me.

[jhenderson]

Rebase.

[jhenderson]

Rebase.

cross-project-tests/CMakeLists.txt

add_llvm_executable(check-gdb-llvm-support
         debuginfo-tests/llvm-prettyprinters/gdb/llvm-support.cpp
 )
 target_link_libraries(check-gdb-llvm-support PRIVATE LLVMSupport)
 
 set(CROSS_PROJECT_TESTS_SOURCE_DIR ${CMAKE_CURRENT_SOURCE_DIR})
 set(CROSS_PROJECT_TESTS_BINARY_DIR ${CMAKE_CURRENT_BINARY_DIR})
 
 set(CROSS_PROJECT_TEST_DEPS
-  clang
   FileCheck
   count
   llvm-config
   llvm-objdump
   check-gdb-llvm-support
   not
   )
 
+if ("clang" IN_LIST LLVM_ENABLE_PROJECTS)
+  list(APPEND CROSS_PROJECT_TEST_DEPS clang)
+endif()
+
 if ("mlir" IN_LIST LLVM_ENABLE_PROJECTS)
   add_llvm_executable(check-gdb-mlir-support
         debuginfo-tests/llvm-prettyprinters/gdb/mlir-support.cpp
   )
   target_include_directories(check-gdb-mlir-support PRIVATE
                                ${LLVM_EXTERNAL_MLIR_SOURCE_DIR}/include
                                ${LLVM_BINARY_DIR}/tools/mlir/include)
   target_link_libraries(check-gdb-mlir-support PRIVATE MLIRIR)

cross-project-tests/debuginfo-tests/lit.local.cfg

+if 'clang' not in config.available_features:
+    config.unsupported = True

cross-project-tests/lit.cfg.py

if is_msvc:
     llvm_config.with_environment('_NT_SYMBOL_PATH', '')
     tools.append(ToolSubst('%cdb', '"%s"' % os.path.join(win_sdk, 'Debuggers',
                                                          arch, 'cdb.exe')))
 
 # clang_src_dir and lld_src_dir are not used by these tests, but are required by
 # use_clang() and use_lld() respectively, so set them to "", if needed.
 if not hasattr(config, 'clang_src_dir'):
     config.clang_src_dir = ""
-llvm_config.use_clang()
+llvm_config.use_clang(required=('clang' in config.llvm_enabled_projects))
+
 if 'lld' in config.llvm_enabled_projects:
     if not hasattr(config, 'lld_src_dir'):
         config.lld_src_dir = ""
     llvm_config.use_lld()
 
 if config.llvm_use_sanitizer:
     # Propagate path to symbolizer for ASan/MSan.
     llvm_config.with_system_environment(