[libc++][test] Prefers the newer clang-tidy version.

[Mordante]

Summary

Module require Clang 17, since Clang 16 requires the magic # FILE
line. Therefore, if available, use clang-tidy 17 too. This change should
be reverted after LLVM 17 is released.

[Mordante]

Trigger CI.

[Mordante]

Adds an extra test.
Rebased on top of D151223.

[ldionne]

I just spoke to Mark and he explained that this was necessary for the C++20 Modules work.

This is not policy-setting like in https://discourse.llvm.org/t/frc-versions-of-libc-clang-format-and-clang-tidy-dependencies/70953, this patch is basically a one-off required to unblock the modules work. If we end up deciding to use ToT clang-tidy after the RFC, then this patch would become permanent and not just a temporary workaround. Otherwise, it's just a temporary workaround since we require some recent clang-tidy features.

In light of this, I am OK with this patch but I do expect that after we land LLVM 17, we'll update the code base to reflect the consensus gained in the RFC (which might mean basically reverting this patch).

libcxx/test/tools/clang_tidy_checks/CMakeLists.txt

8–12

libcxx/test/tools/clang_tidy_checks/CMakeLists.txt

 
-# Look for the latest package
-set(CMAKE_FIND_PACKAGE_SORT_ORDER NATURAL)
-set(CMAKE_FIND_PACKAGE_SORT_DIRECTION DEC)
-
 # The find_package changes these variables. This leaves the build in an odd
 # state. Calling cmake a second time tries to write site config information in
 # the system's libc++. Restoring these setting after testing fixes this issue.
 set(LLVM_DIR_SAVE ${LLVM_DIR})
 set(Clang_DIR_SAVE ${Clang_DIR})
 
-find_package(Clang 16)
-if (NOT Clang_FOUND)
-  find_package(Clang 17)
+# TODO LLVM 17 prefer to use teh stable release again instead of ToT.
+# libc++ normally prefers the use the last stable release instead of the ToT.
+# For modules we need ToT since they are still under heavy development. So
+# temporary the ToT version is preferred.
+if (NOT Clang_FOUND)
+  find_package(Clang 16)
 endif()
 
 set(SOURCES
     abi_tag_on_virtual.cpp
     hide_from_abi.cpp
     proper_version_checks.cpp
     qualify_declval.cpp
     robust_against_adl.cpp

libcxx/utils/libcxx/test/features.py

try:
         if (
             runScriptExitCode(
                 cfg, ["stat %{test-tools}/clang_tidy_checks/libcxx-tidy.plugin"]
             )
             != 0
         ):
             return None
 
+        # TODO MODULES require ToT due module specific fixes.
+        if runScriptExitCode(cfg, ['clang-tidy-17 --version']) == 0:
+          return 'clang-tidy-17'
+
         # TODO This should be the last stable release.
         # LLVM RELEASE bump to latest stable version
         if runScriptExitCode(cfg, ["clang-tidy-16 --version"]) == 0:
             return "clang-tidy-16"
 
         # LLVM RELEASE bump version
         if (
             int(