Make it possible to turn off each of the Windows oldnames workarounds.

Make it possible to turn off each of the Windows oldnames workarounds.

* lib/fcntl.in.h (creat, open):  Conditionalize each of the Windows
oldnames workarounds through a GNULIB_MDA_<func> symbol.
* lib/math.in.h (j0, j1, jn, y0, y1, yn): Likewise.
* lib/search.in.h (lfind, lsearch): Likewise.
* lib/stdio.in.h (fcloseall, fdopen, fileno, getw, putw, tempnam):
Likewise.
* lib/stdlib.in.h (ecvt, fcvt, gcvt, mktemp, putenv): Likewise.
* lib/string.in.h (memccpy, strdup): Likewise.
* lib/sys_stat.in.h (chmod, umask): Likewise.
* lib/time.in.h (tzset): Likewise.
* lib/unistd.in.h (access, chdir, close, dup, dup2, execl, execle,
execlp, execv, execve, execvp, execvpe, getcwd, getpid, isatty, lseek,
read, rmdir, swab, unlink, write): Likewise.
* lib/utime.in.h (utime): Likewise.
* lib/wchar.in.h (wcsdup): Likewise.
* m4/fcntl_h.m4 (gl_FCNTL_H_DEFAULTS): Initialize these
GNULIB_MDA_<func> symbols.
* m4/math_h.m4 (gl_MATH_H_DEFAULTS): Likewise.
* m4/search_h.m4 (gl_SEARCH_H_DEFAULTS): Likewise.
* m4/stdio_h.m4 (gl_STDIO_H_DEFAULTS): Likewise.
* m4/stdlib_h.m4 (gl_STDLIB_H_DEFAULTS): Likewise.
* m4/string_h.m4 (gl_HEADER_STRING_H_DEFAULTS): Likewise.
* m4/sys_stat_h.m4 (gl_SYS_STAT_H_DEFAULTS): Likewise.
* m4/time_h.m4 (gl_HEADER_TIME_H_DEFAULTS): Likewise.
* m4/unistd_h.m4 (gl_UNISTD_H_DEFAULTS): Likewise.
* m4/utime_h.m4 (gl_UTIME_H_DEFAULTS): Likewise.
* m4/wchar_h.m4 (gl_WCHAR_H_DEFAULTS): Likewise.
* modules/fcntl-h (Makefile.am): Substitute these GNULIB_MDA_<func>
symbols.
* modules/math (Makefile.am): Likewise.
* modules/search (Makefile.am): Likewise.
* modules/stdio (Makefile.am): Likewise.
* modules/stdlib (Makefile.am): Likewise.
* modules/string (Makefile.am): Likewise.
* modules/sys_stat (Makefile.am): Likewise.
* modules/time (Makefile.am): Likewise.
* modules/unistd (Makefile.am): Likewise.
* modules/utime-h (Makefile.am): Likewise.
* modules/wchar (Makefile.am): Likewise.