Refine definitions for wchar_t/wint_t on VxWorks

This change refines the VxWorks macro definitions configuring
wchar_t to accommodate the VxWorks7 environment, where wchar_t
is now typically a 32bit type.

We also ensure that the definitions for wint_t are always based
on those for wchar_t, so the two remain in sync in environments
where WCHAR_TYPE is redefined for a specific CPU architecture.

2019-12-30  Alexandre Oliva  <oliva@adacore.com>
           Olivier Hainque  <hainque@adacore.com>

	* config/vx-common.h (WCHAR_TYPE_SIZE): 32 on VxWorks 7.
	(WCHAR_TYPE): Pick accordingly.
	(WINT_TYPE_SIZE): Define in terms of WCHAR_TYPE_SIZE.
	(WINT_TYPE): Define in terms of WCHAR_TYPE.

Co-Authored-By: Olivier Hainque <hainque@adacore.com>

From-SVN: r279780