PAC_PROG_F77_LIBRARY_DIR_FLAG
Determine the flag used to indicate the directories to find libraries in
Notes
Many compilers accept -Ldir just like most C compilers.
Unfortunately, some (such as some HPUX Fortran compilers) do not,
and require instead either -Wl,-L,dir or something else. This
command attempts to determine what is accepted. The flag is
placed into F77_LIBDIR_LEADER.