libconfig: Update to version 1.8

libconfig: Update to version 1.8

- Update from version 1.7.3 to 1.8
- Update of rootfile
- Changelog
    1.8
	  - Added support for binary integer values
	  - Miscellaneous code cleanup
    1.7.4
	  - Handle malloc failures by calling a fatal error handler
	  - New API to provide alternative fatal error handler
	  - Bugfixes to lookup (by name or path) routines
	  - Bugfixes to APIs with inconsistent const-ness
	  - Bugfixes to APIs with inconsistent use of short/unsigned short
	  - Bugfixes to int/int64 auto-conversion
	  - Various cleanup/fixes to build files
	  - Added some unit tests

Signed-off-by: Adolf Belka <adolf.belka@ipfire.org>
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>