vxworks float EFs not precise enough -> use long float

vxworks float EFs not precise enough -> use long float

Some acats-4 tests that check the precision of Float elementary
functions fail with vxworks 7.2's implementations of single-precision
math functions.

This patch arranges for us to bypass the single-precision functions,
and use the Aux_Long_Float implementation, based on the double-typed
calls from the C library, for Float and Short_Float.

for  gcc/ada/ChangeLog

	* Makefile.rtl (LIBGNAT_TARGET_PAIRS): Use Long Float-based
	variant of Aux_Short_Float and Aux_Float on vxworks targets.
	* libgnat/a-nashfl__wraplf.ads: New.
	* libgnat/a-nuaufl__wraplf.ads: New.