Don’t set RUNPATH if it is the system search path - CMAKE_SKIP_RPATH

[heitbaum]

The following encfs commit forces RPATH 31e302c on Linux.

encfs/CMakeLists.txt

Lines 322 to 323 in c444f9b

	# Set RPATH to library install path.
	set(CMAKE_INSTALL_RPATH "${CMAKE_INSTALL_PREFIX}/${LIB_INSTALL_DIR}")

With the cleanup of RPATH/RUNPATH in - LibreELEC/LibreELEC.tv#6094 - we are cleaning up incorrect and unnecessary RPATH/RUNPATH, we have used the CMAKE_SKIP_RPATH build option but given that encfs and encfsctl are including the system search path - the RUNPATH is unnecessary.

reading:

• https://gitlab.kitware.com/cmake/community/-/wikis/doc/cmake/RPATH-handling

Suggest that RUNPATH can still be used when installing, but only if it's not a system directory (as per the wiki) so that it is not necessary to use CMAKE_SKIP_RPATH

 # readelf --dynamic /usr/bin/encfs | grep '\['
 0x0000000000000001 (NEEDED)             Shared library: [libfuse.so.2]
 0x0000000000000001 (NEEDED)             Shared library: [libssl.so.3]
 0x0000000000000001 (NEEDED)             Shared library: [libcrypto.so.3]
 0x0000000000000001 (NEEDED)             Shared library: [libstdc++.so.6]
 0x0000000000000001 (NEEDED)             Shared library: [libgcc_s.so.1]
 0x0000000000000001 (NEEDED)             Shared library: [libc.so.6]
 0x000000000000001d (RUNPATH)            Library runpath: [/usr/lib]

readelf --dynamic /usr/bin/encfsctl | grep '\['
 0x0000000000000001 (NEEDED)             Shared library: [libfuse.so.2]
 0x0000000000000001 (NEEDED)             Shared library: [libssl.so.3]
 0x0000000000000001 (NEEDED)             Shared library: [libcrypto.so.3]
 0x0000000000000001 (NEEDED)             Shared library: [libstdc++.so.6]
 0x0000000000000001 (NEEDED)             Shared library: [libgcc_s.so.1]
 0x0000000000000001 (NEEDED)             Shared library: [libc.so.6]
 0x000000000000001d (RUNPATH)            Library runpath: [/usr/lib]

# LD_LIBRARY_PATH= LD_DEBUG=libs ldd -v encfs