Support compiling without -loldnames on native Windows.

Support compiling without -loldnames on native Windows.

* m4/gnulib-common.m4 (GL_MDA_DEFINES, _GL_MDA_DEFINES): New macros.
* m4/chown.m4 (AC_FUNC_CHOWN): In the test programs, use GL_MDA_DEFINES.
(gl_FUNC_CHOWN, gl_FUNC_CHOWN_FOLLOWS_SYMLINK): Likewise.
* m4/dup.m4 (gl_FUNC_DUP): Likewise.
* m4/dup2.m4 (gl_FUNC_DUP2): Likewise.
* m4/fchdir.m4 (gl_FUNC_FCHDIR): Likewise.
* m4/fchmodat.m4 (gl_FUNC_FCHMODAT): Likewise.
* m4/fchownat.m4 (gl_FUNC_FCHOWNAT_EMPTY_FILENAME_BUG): Likewise.
* m4/fcntl-o.m4 (gl_FCNTL_O_FLAGS): Likewise.
* m4/fcntl.m4 (gl_FUNC_FCNTL): Likewise.
* m4/fdopen.m4 (gl_FUNC_FDOPEN): Likewise.
* m4/fdopendir.m4 (gl_FUNC_FDOPENDIR): Likewise.
* m4/fflush.m4 (gl_FUNC_FFLUSH_STDIN): Likewise.
* m4/fopen.m4 (gl_FUNC_FOPEN_GNU): Likewise.
* m4/freopen.m4 (gl_FUNC_FREOPEN): Likewise.
* m4/futimens.m4 (gl_FUNC_FUTIMENS): Likewise.
* m4/getcwd-abort-bug.m4 (gl_FUNC_GETCWD_ABORT_BUG): Likewise.
* m4/getcwd-path-max.m4 (gl_FUNC_GETCWD_PATH_MAX): Likewise.
* m4/getcwd.m4 (gl_FUNC_GETCWD_NULL, gl_FUNC_GETCWD_SIGNATURE):
Likewise.
* m4/getdtablesize.m4 (gl_FUNC_GETDTABLESIZE): Likewise.
* m4/linkat.m4 (gl_FUNC_LINKAT): Likewise.
* m4/lseek.m4 (gl_FUNC_LSEEK): Likewise.
* m4/mkdir.m4 (gl_FUNC_MKDIR): Likewise.
* m4/mkstemp.m4 (gl_FUNC_MKSTEMP): Likewise.
* m4/mktime.m4 (gl_FUNC_MKTIME_WORKS): Likewise.
* m4/open-slash.m4 (gl_OPEN_TRAILING_SLASH_BUG): Likewise.
* m4/poll.m4 (gl_FUNC_POLL): Likewise.
* m4/posix_spawn.m4 (gl_POSIX_SPAWN_WORKS): Likewise.
* m4/pread.m4 (gl_FUNC_PREAD): Likewise.
* m4/pselect.m4 (gl_FUNC_PSELECT): Likewise.
* m4/pthread_sigmask.m4 (gl_FUNC_PTHREAD_SIGMASK): Likewise.
* m4/ptsname_r.m4 (gl_PREREQ_PTSNAME_R): Likewise.
* m4/putenv.m4 (gl_FUNC_PUTENV): Likewise.
* m4/pwrite.m4 (gl_FUNC_PWRITE): Likewise.
* m4/rename.m4 (gl_FUNC_RENAME): Likewise.
* m4/rmdir-errno.m4 (gl_FUNC_RMDIR_NOTEMPTY): Likewise.
* m4/rmdir.m4 (gl_FUNC_RMDIR): Likewise.
* m4/select.m4 (gl_FUNC_SELECT): Likewise.
* m4/setenv.m4 (gl_FUNC_UNSETENV): Likewise.
* m4/strncat.m4 (gl_FUNC_STRNCAT): Likewise.
* m4/ttyname_r.m4 (gl_FUNC_TTYNAME_R): Likewise.
* m4/unlink-busy.m4 (gl_FUNC_UNLINK_BUSY_TEXT): Likewise.
* m4/unlink.m4 (gl_FUNC_UNLINK): Likewise.
* m4/utimens.m4 (gl_UTIMENS): Likewise.
* m4/utimensat.m4 (gl_FUNC_UTIMENSAT): Likewise.
* m4/utimes.m4 (gl_FUNC_UTIMES): Likewise.
* m4/canonicalize.m4 (gl_CANONICALIZE_LGPL): On native Windows, don't
test for getcwd.
* m4/utime.m4 (gl_FUNC_UTIME): On native Windows, don't test for utime.
* m4/wcsdup.m4 (gl_FUNC_WCSDUP): To test for wcsdup, use a test program
with GL_MDA_DEFINES.
* lib/c++defs.h (_GL_CXXALIAS_MDA): New macro.
* lib/fcntl.in.h (creat, open):  On native Windows, use the underscore-
prefixed symbol.
* 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.
* lib/math.in.h (j0, j1, jn, y0, y1, yn):  Likewise.
(isfinite, isinf, isnan, signbit): On native Windows, don't define as an
rpl_-prefixed macro.
* lib/canonicalize-lgpl.c (__getcwd): On native Windows, use _getcwd.
* lib/close.c (close_nothrow): On native Windows, use _close.
* lib/creat.c (orig_creat): On native Windows, use _creat.
* lib/dup.c (dup_nothrow): On native Windows, use _dup.
* lib/dup2.c (dup2_nothrow): Use _dup2.
* lib/fdopen.c (fdopen_nothrow): On native Windows, use _fdopen.
* lib/getcwd-lgpl.c: On native Windows, use _getcwd.
* lib/getcwd.c (getcwd_nothrow): Use _getcwd also on mingw.
* lib/open.c (orig_open): On native Windows, use _open.
* lib/read.c (read_nothrow): Use _read.
* lib/rmdir.c: On native Windows, use _rmdir.
* lib/unlink.c: On native Windows, use _unlink.
* lib/write.c (write_nothrow): Use _write.
* lib/sys_select.in.h (close): With clang, don't attach a warning on an
undefined symbol.
* lib/sys_socket.in.h (close): Likewise.
* lib/sys_time.in.h (close): Likewise.
* tests/test-spawn-pipe-child.c: On native Windows, use _fdopen.