LD: Avoid a division by zero page size with SEGMENT_START handling

LD: Avoid a division by zero page size with SEGMENT_START handling

Avoid a division by zero and thus a linker crash in SEGMENT_START script
builtin function handling, by not checking the value supplied with a
`-T' command-line override against the maximum page size if that has not
been set.

	ld/
	* ldexp.c (fold_binary): Check that `config.maxpagesize' is
	non-zero before using it as a divisor.