Provide vxworks alternate stdint.h during the build

Provide vxworks alternate stdint.h during the build

This change arranges to provide the vxworks alternate stdint.h
at build time instead of at install time, so it is used instead
of the system one while building the libraries.

This is a lot more consistent and helps the build on configurations
where the system does not come with stdint.h at all.

The change uses a similar mechanism as the one previsouly introduced
for glimits.h and takes the opportunity to simplify the glimits.h
command to use an automatic variable.

This introduces an indirect dependency on the VxWorks version.h
for vxcrtstuff objects, for which we then need to apply the same
tricks as for libgcc2 regarding include paths (to select the system
header instead of the gcc one).

2021-02-12  Olivier Hainque  <hainque@adacore.com>
	    Rasmus Villemoes  <rv@rasmusvillemoes.dk>

gcc/
	* Makefile.in (T_STDINT_GCC_H): New variable, path to
	stdint-gcc.h that a target configuration may override when
	use_gcc_stdint is "provide".
	(stmp-int-hdrs): Depend on it and copy that for
	USE_GCC_INT=provide.
	* config.gcc (vxworks): Revert to use_gcc_stdint=provide.
	* config/t-vxworks (T_STDINT_GCC_H): Define, as vxw-stdint-gcc.h.
	(vxw-stdint-gcc.h): New target, produced from the original
	stdint-gcc.h.
	(vxw-glimits.h): Use an automatic variable to designate the
	first and only prerequisite.
	* config/vxworks/stdint.h: Remove.

libgcc/
	* config/t-vxworks: Set CRTSTUFF_T_CFLAGS to
	$(LIBGCC2_INCLUDES).
	* config/t-vxworks7: Likewise.