[libc++][CMake] Adds option to disable clang-tidy.

There have been some reports that always enabling clang-tidy (added in
llvm#90077) has some false positives in the detection. It would be good to fix
these. This adds an escape hatch to disable the tests, which avoids
blocking users with this issue.

libcxx/CMakeLists.txt

@@ -60,6 +60,10 @@ option(LIBCXX_ENABLE_FILESYSTEM
    available on the platform. This includes things like most parts of <filesystem> and
    others like <fstream>" ON)
 option(LIBCXX_INCLUDE_TESTS "Build the libc++ tests." ${LLVM_INCLUDE_TESTS})
+option(LIBCXX_DISABLE_CLANG_TIDY_TESTS
+  "Disables test using the clang-tidy plugin. This option should only be used
+   when autodetection fails, please file a bug report so the autodetection can
+   be improved." OFF)
 set(LIBCXX_SUPPORTED_HARDENING_MODES none fast extensive debug)
 set(LIBCXX_HARDENING_MODE "none" CACHE STRING
   "Specify the default hardening mode to use. This mode will be used inside the

libcxx/test/tools/CMakeLists.txt

@@ -5,4 +5,8 @@ if(NOT CMAKE_CXX_COMPILER_ID STREQUAL "Clang")
   message(STATUS "Clang-tidy tests are disabled due to non-clang based compiler.")
   return()
 endif()
+if(LIBCXX_DISABLE_CLANG_TIDY_TESTS)
+  message(STATUS "Clang-tidy tests are disabled by the configuration option LIBCXX_DISABLE_CLANG_TIDY_TESTS.")
+  return()
+endif()
 add_subdirectory(clang_tidy_checks)