intptr_t type definition needed

coffcode.h uses an intptr_t cast inside an #ifdef RS6000COFF_C, so
ensure that intptr_t is defined.  We don't see this when
cross-compiling from linux due to intptr_t being provided by
unistd.h.

	PR 16686
	* coff-rs6000.c: Include stdint.h.
	* coff64-rs6000.c: Likewise.