[clang] Remove HelpHidden from the -resource-dir option (llvm#163131)

Currently the "getter" option `-print-resource-dir` is visible when
typing `--help`, but the corresponding "setter" option `-resource-dir`
is not.

This option is useful when one is using clang on a non-standard
location, or when one is building a libtooling-based tool (e.g. IWYU)
based on a local clang build. In that case, we need to specify the
correct path to the resource directory for things to work.

Existing documentation already makes use of this option, for example
here:


https://clang.llvm.org/docs/StandardCPlusPlusModules.html#possible-issues-failed-to-find-system-headers

There is thus no reason to keep this option hidden from the help and
documentation.

---------

Co-authored-by: Carlos Gálvez <[email protected]>

Author: carlosgalvezp

clang/docs/ReleaseNotes.rst

@@ -276,7 +276,7 @@ New Compiler Flags
 - New option ``-fno-sanitize-debug-trap-reasons`` added to disable emitting trap reasons into the debug info when compiling with trapping UBSan (e.g. ``-fsanitize-trap=undefined``).
 - New option ``-fsanitize-debug-trap-reasons=`` added to control emitting trap reasons into the debug info when compiling with trapping UBSan (e.g. ``-fsanitize-trap=undefined``).
 - New options for enabling allocation token instrumentation: ``-fsanitize=alloc-token``, ``-falloc-token-max=``, ``-fsanitize-alloc-token-fast-abi``, ``-fsanitize-alloc-token-extended``.
-
+- The ``-resource-dir`` option is now displayed in the list of options shown by ``--help``.
 
 Lanai Support
 ^^^^^^^^^^^^^^

clang/include/clang/Driver/Options.td

@@ -6122,7 +6122,7 @@ def rewrite_legacy_objc : Flag<["-"], "rewrite-legacy-objc">,
 def rdynamic : Flag<["-"], "rdynamic">, Group<Link_Group>,
   Visibility<[ClangOption, FlangOption]>;
 def resource_dir : Separate<["-"], "resource-dir">,
-  Flags<[NoXarchOption, HelpHidden]>,
+  Flags<[NoXarchOption]>,
   Visibility<[ClangOption, CC1Option, CLOption, DXCOption, FlangOption, FC1Option]>,
   HelpText<"The directory which holds the compiler resource files">,
   MarshallingInfoString<HeaderSearchOpts<"ResourceDir">>;