float128: Extend the power of ten tables

float128: Extend the power of ten tables

Update the power of ten tables used by the common implementation when long
double is not the most expressive real type.

	* stdlib/fpioconst.h: Include bits/floatn.h.
	(FPIOCONST_HAVE_EXTENDED_RANGE): New macro for testing how big the
	power of ten table should be.
	(FPIOCONST_POW10_ARRAY_SIZE): Use larger table if above is true.
	* stdlib/fpioconst.c (__tens): Use FPIOCONST_HAVE_EXTENDED_RANGE
	to include larger tables when _Float128 support is enabled.
	(_fpioconst_pow10): Likewise.