relocatable-prog: Use wrapper-free installation also on Mac OS X. Reported by Paul Smith <psmith@gnu.org>. * build-aux/install-reloc: Accept a 'mode' argument as first argument. (func_relativize): New function, from gnulib-tool. Handle mode 'macosx' through invocations of 'otool' and 'install_name_tool'. * m4/relocatable.m4 (gl_RELOCATABLE_BODY): Determine use_macos_tools. If use_macos_tools is true, set INSTALL_PROGRAM_ENV to an 'install-reloc' invocation with mode 'macosx'.