cobol: Implement and use faster __gg__packed_to_binary() routine.

cobol: Implement and use faster __gg__packed_to_binary() routine.

The new routine uses table lookups more effectively, and avoids __int128
arithmetic until necessary.

gcc/cobol/ChangeLog:

	* genutil.cc (get_binary_value): Use the new routine.

libgcobol/ChangeLog:

	* libgcobol.cc (get_binary_value_local): Use the new routine.
	* stringbin.cc (int_from_string): Removed.
	(__gg__packed_to_binary): Implement new routine.
	* stringbin.h (__gg__packed_to_binary): Likewise.