* Makerules: Always use -MP together with -MD.
	(sed-remove-dotot): Substitute $(..) also at start of line.
	($(stdio_lim:h=st)): Use -MD instead of SUNPRO_DEPENDENCIES.
	Generated defines with a single compiler call.
	Use $(sed-remove-dotdot).
	* mach/Makefile ($(objpfx)mach-syscalls.mk): Use -MD instead
	of DEPENDENCIES_OUTPUT, and use $(sed-remove-objpfx).
	* sysdeps/unix/sysv/linux/Makefile ($(objpfx)syscall-%.h):
	Use -MD instead of SUNPRO_DEPENDENCIES, and use $(sed-remove-objpfx).
	* sysdeps/unix/sysv/linux/mips/Makefile
	($(objpfx)syscall-%.h): Likewise.