elfcompress: Don't over allocate sections bitmap

elfcompress: Don't over allocate sections bitmap

In process_file we allocate a bitmap sections to track which sections
we want to (de)compress. This allocates shnum / 8 + 1 unsigned
ints. But an unsigned int can contain more bits than just 8. In all
other places we use WORD_BITS defined as 8U * sizeof (unsigned int).
Also use WORD_BITS to calculate how many unsigned ints we need for the
sections bitmap.

	* src/elfcompress.c (process_file): Use shnum / WORD_BITS + 1
	to allocate sections.

Signed-off-by: Mark Wielaard <mark@klomp.org>