[gettext] Couldn't adjust RPATH on macOS

[jdpurcell]

Running this command from an ARM64 macOS host:
vcpkg install gettext[tools]

Used to, i.e. with a2938d0 (2024-07-26) or older, produce output such as:

-- Remove RPATH from '/Users/runner/work/kimageformats-binaries/kimageformats-binaries/vcpkg/packages/gettext_arm64-osx/lib/gettext/cldr-plurals' ('@loader_path/..')
-- Adjusted RPATH of '/Users/runner/work/kimageformats-binaries/kimageformats-binaries/vcpkg/packages/gettext_arm64-osx/lib/gettext/cldr-plurals' (To '@loader_path/..')

With a68201b (2024-07-27) or anything after, it started producing output such as:

CMake Warning at scripts/cmake/z_vcpkg_fixup_rpath_macho.cmake:157 (message):
Warning:   Couldn't adjust RPATH of
  '/Users/runner/work/kimageformats-binaries/kimageformats-binaries/vcpkg/packages/gettext_arm64-osx/lib/gettext/cldr-plurals':
  Usage:
  /Applications/Xcode_15.3.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/install_name_tool
  [-change old new] ...  [-rpath old new] ...  [-add_rpath new] ...
  [-delete_rpath old] ...  [-id name] input

Call Stack (most recent call first):
  scripts/ports.cmake:205 (z_vcpkg_fixup_macho_rpath_in_dir)