The printf(3) format string character "%m" is available on
Linux/glibc and FreeBSD, but not on MacOSX. So using "%m"
should be limited to system specific code.
Documents the use of GP_CAMLIB_SET on the make command line.
Setting CAMLIBS= on the make command line to specify the set of
camlibs to be built and installed has not worked at least since
the introduction of GP_CAMLIB_SET.