* 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.
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