Document implemented functions

	* posix.xml (std-susv4): Add newly implemented math SUSv4 math
	functions.  Add missing functions strtold and tcgetsid.  Re-sort.
	(std-gnu): Add clog10l, exp10l, pow10l, sincos{f,l}.
	(std-notimpl): Drop now implemented functions.

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