* cygheap.h (cwdstuff): Convert to class. Make posix and dir private.

	* cygheap.h (cwdstuff): Convert to class.  Make posix and dir private.
	(cwdstuff::get_posix): New method.
	(cwdstuff::reset_posix): New method.
	* dcrt0.cc (dll_crt0_1): Call setlocale rather than _setlocale_r.
	* environ.cc (environ_init): Ditto.  Prefer "C" locale over current
	codepage default locale.
	* path.cc (chdir): Use cwdstuff::get_posix method instead of accessing
	cwdstuff::posix directly.
	(cwdstuff::set): Defer creating posix path to first usage.
	(cwdstuff::get_posix): Create posix path if it's empty, and return it.
	(cwdstuff::get): Create posix path if it's empty.
	* strfuncs.cc (sys_cp_wcstombs): Use UTF-8 conversion in the "C"
	locale.
	(sys_cp_mbstowcs): Ditto.
	* syscalls.cc (gen_full_path_at): Fetch CWD posix path locked.
	(setlocale): Implement here.  Reset CWD posix path.