libgcobol: Fix bootstrap for targets without program_invocation_short_name

libgcobol: Fix bootstrap for targets without program_invocation_short_name

program_invocation_short_name is not widely available, however getprogname()
appears to be a suitable replacement.

Amend the library configuration to look for both. Use program_invocation_short_name
in preference to getprogname() when it is available.  If neither is found fall
back to a constant string.

libgcobol/ChangeLog:

	* config.h.in: Regenerate.
	* configure: Regenerate.
	* configure.ac: Check for program_invocation_short_name and
	and getprogname().
	* libgcobol.cc (default_exception_handler): When the platform
	has program_invocation_short_name, use it otherwise fall
	back to using getprogname() or a constant string (if neither
	interface is available).

Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>