[package] mpir/3.0.0: rpath is incorrect on macOS with shared library option

[ikoruk]

Package and Environment Details (include every applicable attribute)

• Package Name/Version: mpir/3.0.0
• Operating System+version: MacOS 10.15.5
• Compiler+version: Apple clang version 11.0.3
• Conan version: conan 1.25.2
• Python version: Python 3.7.7

Conan profile (output of conan profile show default or conan profile show <profile> if custom profile is in use)

[settings]
os=Macos
os_build=Macos
arch=x86_64
arch_build=x86_64
compiler=apple-clang
compiler.version=11.0
compiler.libcxx=libc++
build_type=Release
cppstd=14
[options]
[build_requires]
[env]

Steps to reproduce (Include if Applicable)

Downloading the prebuilt versions, with the shared library option (used by packages like CGAL), causes a dynamic linking error since the rpath is not set correctly, causing errors like those in the logs.

Additionally, compiling from source only fixes the problem locally since it refers to itself as its absolute path, but it doesn't allow for distribution of the prebuilt package either.

Logs (Include/Attach if Applicable)

Click to expand log

dyld: Library not loaded: /tmp/c3ipr/pr_1532_4_0_98/.conan/data/mpir/3.0.0/_/_/package/750e1dcf4c97ff4f414802c71282d79d7405a340/lib/libmpir.23.dylib

[SpaceIm]

@uilianries this issue has been fixed by #9135