Genex LINK_LIBRARY: fix some definitions for Apple platforms

Some declarations were inconsistent.
For example, "LINKER:-force_load <LIBRARY>" was translated to
"-Xlinker -force_load /path/to/library". The correct translation
should be "-Xlinker -force_load -Xlinker /path/to/library" because
the library is an argument to the -force_load option.