provide a workaround if program_invocation_short_name is missing

provide a workaround if program_invocation_short_name is missing

Try some replacements, such as getexecname() on Solaris and __progname
on BSDs and Darwin.  When not found, base program_invocation_short_name
on the source filename it is used in, as not to require argv[0] to be
passed along.  This latter approach is not dynamic, but doesn't require
code changes for all places where program_invocation_short_name is used
now.

Signed-off-by: Fabian Groffen <grobian@gentoo.org>
Signed-off-by: Karel Zak <kzak@redhat.com>