gas various other void* casts

gas various other void* casts

This removes assorted unneeded casts of void* pointers, and casts when
passing args to void* parameters or storing to void* pointers.  The
patch also changes obj-coff.c stack_push to take a void* parameter,
and replaces an odd memcpy in tc-metag.c find_insn_templates with a
simple assignment.