Support defining strtof32, wcstof32 aliases.

Support defining strtof32, wcstof32 aliases.

This patch adds support for defining strtof32, wcstof32, strtof32_l
and wcstof32_l functions as aliases of the corresponding float
functions when _Float32 support is enabled.

Tested for x86_64; also tested with build-many-glibcs.py in
conjunction with other _Float32 changes.

	* stdlib/strtof.c: Include <bits/floatn.h>
	[__HAVE_FLOAT32 && !__HAVE_DISTINCT_FLOAT32] (strtof32): Define
	and later undefine as macro.  Define as weak alias if
	[!USE_WIDE_CHAR].
	[__HAVE_FLOAT32 && !__HAVE_DISTINCT_FLOAT32] (wcstof32): Define
	and later undefine as macro.  Define as weak alias if
	[USE_WIDE_CHAR].
	* stdlib/strtof_l.c: Include <bits/floatn.h>
	[__HAVE_FLOAT32 && !__HAVE_DISTINCT_FLOAT32] (strtof32_l): Define
	and later undefine as macro.  Define as weak alias if
	[!USE_WIDE_CHAR].
	[__HAVE_FLOAT32 && !__HAVE_DISTINCT_FLOAT32] (wcstof32_l): Define
	and later undefine as macro.  Define as weak alias if
	[USE_WIDE_CHAR].