Import correctly working strtold from David M. Gay.

Import correctly working strtold from David M. Gay.

	* libc/stdlib/Makefile.am (GENERAL_SOURCES): Add strtodg.c and
	strtorx.c.
	* libc/stdlib/Makefile.in: Regenerate.
	* libc/stdlib/strtodg.c: New file implementing generic string to long
	double conversion.
	* libc/stdlib/strtorx.c: New file, implementing IEEE format string to
	long double conversion.
	* libc/stdlib/mprec.h (_strtodg_r): Declare.
	(_strtorx_r): Declare.
	* libc/stdlib/gdtoa.h (__UShort): Define.
	* libc/stdlib/strtold.c (__flt_rounds): Define for i386 and x86_64
	target.
	(FLT_ROUNDS): Define, as 0 on platforms missing a __flt_rounds
	function.
	(_strtold_r): Converted from strtold.  Call _strtorx_r on targets
	supporting distinct long doubles.
	(strtold): Just call _strtold_r.
	* libc/include/stdlib.h (_strtold_r): Declare.
	* libc/stdlib/ldtoa.c (_strtold): Comment out.  Explain why.
	* libc/stdio/vfscanf.c (__SVFSCANF_R): Call _strtold_r instead of
	_strtold.
	* libc/machine/powerpc/vfscanf.c (__svfscanf_r): Ditto.

	* common.din (strtold): Drop redirection to _strtold.

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>