Adapt libstdc++ os_defines for VxWorks to more recent versions

This change reworks the VxWorks specific os_defines.h internal
lisbstdc++ header to help fix build and runtime failures of various
kinds in environments from 6.4/6.9 to 7 SR640, based on experiments
and observations conducted against real installs of these OSes for
different CPU architectures.

2019-12-30  Jerome Lambourg  <lambourg@adacore.com>
           Olivier Hainque  <hainque@adacore.com>

	libstdc++
	* config/os/vxworks/os_defines.h
	(NOMINMAX): Always redefine to 1.
	(_NO_CPP_INLINES): Likewise.
	(_GLIBCXX_USE_WEAK_REF): Define to 1 for RTP on
	VxWorks >= 7, to 0 otherwise.
	(_GLIBCXX_HAVE_TLS): Define to 1.
	For VxWorks >= 7:
	(_GLIBCXX_USE_C99_MATH): Define to 1.
	(_GLIBCXX_USE_C99_MATH_FP_MACROS_DYNAMIC): Define to 0.
	(_HAS_TR1_DECLARATIONS): Redefine to 0.
	For VxWorks < 7, RTP:
	(_GLIBCXX_INCLUDE_NEXT_C_HEADERS): Define to 1.
	(_GLIBCXX_USE_C99_FP_MACROS_DYNAMIC): Redefine to 1.
	(__CORRECT_ISO_CPP11_MATH_H_PROTO_FP): Define.
	For VxWorks < 7, kernel: #include <vxWorks.h>

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

From-SVN: r279792