ARM: gz-plugin2 CLI executable has broken RPATH

[scpeters]

Description:

The executable in gz-plugin2's libexec folder is not able to load the libgz-plugin2-loader.2.dylib library when using an ARM processor with homebrew installed in /opt/homebrew:

$(brew --prefix)/opt/gz-plugin2/libexec/gz/plugin2/gz-plugin
dyld[90133]: Library not loaded: '@rpath/libgz-plugin2-loader.2.dylib'
  Referenced from: '/opt/homebrew/Cellar/gz-plugin2/2.0.1/libexec/gz/plugin2/gz-plugin'
  Reason: tried: '/opt/homebrew/Cellar/gz-plugin2/2.0.1/libexec/gz/plugin2/../lib/libgz-plugin2-loader.2.dylib' (no such file), '/opt/homebrew/Cellar/gz-plugin2/2.0.1/libexec/gz/plugin2/../lib/libgz-plugin2-loader.2.dylib' (no such file), '/usr/local/lib/libgz-plugin2-loader.2.dylib' (no such file), '/usr/lib/libgz-plugin2-loader.2.dylib' (no such file)
Abort trap: 6

Please supply your brew configuration:

$ brew config
HOMEBREW_VERSION: 4.1.11-2-geacdf7a
ORIGIN: https://github.com/Homebrew/brew
HEAD: eacdf7aa60a1a8a64acc71853ec5559cfd2329c3
Last commit: 22 hours ago
Core tap origin: https://github.com/Homebrew/homebrew-core
Core tap HEAD: 6ff75ff4ca4500b187f786536ed90867fa1db3d7
Core tap last commit: 7 hours ago
Core tap branch: master
Core tap JSON: 12 Sep 19:39 UTC
HOMEBREW_PREFIX: /opt/homebrew
HOMEBREW_CASK_OPTS: []
HOMEBREW_MAKE_JOBS: 8
HOMEBREW_SORBET_RUNTIME: set
Homebrew Ruby: 2.6.10 => /System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/bin/ruby
CPU: octa-core 64-bit arm_firestorm_icestorm
Clang: 14.0.0 build 1400
Git: 2.37.1 => /Library/Developer/CommandLineTools/usr/bin/git
Curl: 8.1.2 => /usr/bin/curl
macOS: 12.6.8-arm64
CLT: 14.2.0.0.1.1668646533
Xcode: N/A
Rosetta 2: false

A test for this is being added to the gz-plugin2 formula in #2402, but it is not yet fixed.

[scpeters]

Currently RPATH is added to our homebrew formulae by adding -DCMAKE_INSTALL_RPATH=#{rpath} to the cmake arguments (see gz-plugin2.rb for example). The default value of rpath resolves to "@loader_path/../lib", which works when the @loader_path is a sibling of <prefix>/lib, like <prefix>/bin, but it does not work for <prefix/libexec/gz/plugin2/gz-plugin.

Since specifying CMAKE_INSTALL_RPATH when invoking cmake will apply to all targets within a project, it may be necessary to set INSTALL_RPATH as a property for each target depending on their relative path to the lib folder.