Set install RPATH on macOS so binaries find libopenscap

[edlitmus]

Summary

After make install on macOS, oscap referenced @rpath/libopenscap.<ver>.dylib but the binary had no LC_RPATH entries, so dyld failed at startup:

dyld[…]: Library not loaded: @rpath/libopenscap.33.dylib
  Referenced from: /usr/local/bin/oscap
  Reason: no LC_RPATH's found

The library was installed correctly to /usr/local/lib/libopenscap.33.dylib; the binary just had no way to locate it without DYLD_LIBRARY_PATH. CMake on macOS strips the build-tree RPATH at install time and provides nothing in its place unless CMAKE_INSTALL_RPATH is set.

This adds, inside the existing if(APPLE) block in the root CMakeLists.txt:

• CMAKE_MACOSX_RPATH ON
• CMAKE_INSTALL_NAME_DIR "@rpath"
• CMAKE_INSTALL_RPATH "@loader_path/../lib;${CMAKE_INSTALL_PREFIX}/lib"

@loader_path/../lib keeps the install relocatable; the absolute prefix path is a fallback. Linux and Windows are unaffected — the block is APPLE-only.

This is a follow-on to the macOS/FreeBSD portability work in #2326.

Test plan

• Configure + build cleanly on macOS (Apple Silicon, Homebrew toolchain)
• Staged install (DESTDIR=… make install): otool -l .../bin/oscap shows both LC_RPATH entries (@loader_path/../lib and /usr/local/lib)
• Real install to /usr/local: oscap --version and oscap xccdf generate report … run without DYLD_LIBRARY_PATH
• Linux unaffected (block is gated on APPLE; no CMake variables Linux uses are touched)

No new automated test — existing CI (.github/workflows/) runs on Ubuntu and Fedora only, so an RPATH check wouldn't execute. The fix is verifiable manually with otool -l on macOS.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[Mab879]

Thanks!

The failure on rawhide will be fixed #2347.