configure.ac: Check for getexecname.

	* configure.ac: Check for getexecname.
	* fileline.c: #include <errno.h>.  Define getexecname if not
	available.
	(fileline_initialize): Try to find the executable in a few
	different ways.
	* print.c (error_callback): Only print the filename if it came
	from the backtrace state.
	* configure, config.h.in: Rebuild.

Co-Authored-By: Gerald Pfeifer <gerald@pfeifer.com>
Co-Authored-By: Rainer Orth <ro@CeBiTec.Uni-Bielefeld.DE>

From-SVN: r193454