Lose some COFF/PE static vars, and peicode.h constify

This patch tidies some COFF and PE code that unnecessarily used static
variables to communicate between functions.

	* coffcode.h (pelength, peheader): Delete static variables.
	(coff_apply_checksum): Instead, define them as auto vars, and pass..
	(coff_read_word, coff_compute_checksum): ..to here.  Delete
	unnecessary forward declarations.
	* pei-x86_64.c (pdata_count): Delete static variable.
	(struct pex64_paps): New.
	(pex64_print_all_pdata_sections, pex64_bfd_print_pdata): Pass
	a pex64_paps for counting.
	* peicode.h (jtab): Constify.