Use Gnulib 'tempname' on MS-Windows

Use Gnulib 'tempname' on MS-Windows

* lib-src/ntlib.h (mkdir, open): Remove redefinitions.  They are
now in nt/inc/ms-w32.h.
* lib-src/ntlib.c (sys_mkdir, sys_open): New functions.
(mkostemp): Remove.

* src/w32.c (mkostemp): Remove.
(sys_mkdir): Accept a second (unused) argument.
* src/fileio.c (Fmake_directory_internal): Remove the WINDOWSNT
specific call to mkdir.  (Bug#28023)

* nt/inc/ms-w32.h (mkdir): Remove from "#ifdef emacs" and redefine
to accept 2 arguments.
(open): Remove from "#ifdef emacs".
* nt/mingw-cfg.site (ac_cv_func_mkostemp): Remove.
* nt/gnulib-cfg.mk (OMIT_GNULIB_MODULE_mkostemp)
(OMIT_GNULIB_MODULE_tempname): Remove.