Move inttypes.h and stdint.h to stdlib.

inttypes.h and stdint.h are in sysdeps/generic, but there are no other
versions of these headers anywhere in the source tree, so they aren’t
actually system-dependent.  Move them to the subdirectory that
installs them (stdlib).

Reviewed-by: Joseph Myers <joseph@codesourcery.com>

	* sysdeps/generic/inttypes.h, sysdeps/generic/stdint.h:
	Move to stdlib.
	* include/inttypes.h: Adjust to match.
	* include/stdint.h: New wrapper.