Include string.h.

Include string.h.
(HAVE_FREXP, HAVE_FMOD): Macros removed.
(struct timeval, struct timezone, gettimeofday): Declarations removed.
(HAVE_SOCKETS, MAIL_USE_POP, MAIL_USE_SYSTEM_LOCK): Macros defined.
(DIRECTORY_SEP): Use Vdirectory_sep_char.
(EXEC_SUFFIXES): Add .cmd to list of suffixes.
(EXEC_SUFFIXES): Add .cmd to list of suffixes.
> (HAVE_SYS_TIMEB_H, HAVE_SYS_TIME_H, HAVE_UNISTD_H, STDC_HEADERS,
TIME_WITH_SYS_TIME, HAVE_GETTIMEOFDAY, HAVE_CLOSEDIR,
HAVE_LONG_FILE_NAMES, HAVE_BCOPY, HAVE_BCMP, HAVE_LOGB, HAVE_FREXP,
HAVE_FMOD, HAVE_FTIME, HAVE_MKTIME, HAVE_H_ERRNO): New macros.
(access, chdir, chmod, close, creat, ctime, dup, dup2, fopen,
link, mkdir, mktemp, open, pipe, read, rename, rmdir, select,
sleep, unlink, write, spawnve, wait, kill, signal):
Macros redefined from win32_* to sys_*.
[__STDC__]: Define when including direct.h, io.h, stdio.h.
(struct nt_stat): Definition removed.
(stat, st_dev, st_ino, st_mode, st_nlink, st_uid, st_gid,
st_rdev, st_size, st_atime, st_mtime, st_ctime): Macros undefined.