aarch64-* and ppc*-linux-gnu long long float/long double mismatch

aarch64-* and ppc*-linux-gnu long long float/long double mismatch

Some platforms have failed to build because long long float is mapped
to double rather than long double, and then the attempts to import
intrinsics for long double in Aux_Long_Long_Float raise warnings
turned into errors.

This patch is a work around for the mismatch, arranging for
Aux_Long_Long_Float to map to Aux_Long_Float.

for  gcc/ada/ChangeLog

	* Makefile.rtl (LIBGNAT_TARGET_PAIRS): Use
	a-nallfl__wraplf.ads on aarch64-* and ppc*-linux-gnu targets.
	* libgnat/a-nallfl__wraplf.ads: New.