* doc/posix-functions/isatty.texi: Mention the MSVC problem.
* lib/isatty.c: Include <errno.h>, msvc-inval.h.
(_isatty_nothrow): New function.
(isatty): Use it instead of _isatty.
(IsConsoleHandle): Add comment, from Paolo Bonzini.
* lib/poll.c (IsConsoleHandle): Likewise.
* lib/select.c (IsConsoleHandle): Likewise.
* m4/isatty.m4 (gl_FUNC_ISATTY): Fix comment. Reported by Eli Zaretskii.
(gl_PREREQ_ISATTY): New macro.
* modules/isatty (Depends-on): Add msvc-inval.
(configure.ac): Invoke gl_PREREQ_ISATTY.
* lib/unistd.in.h (isatty): New declaration.
* lib/isatty.c: New file, based on an idea of
Bastien Roucariès <roucaries.bastien@gmail.com>.
* m4/isatty.m4: New file.
* m4/unistd_h.m4 (gl_UNISTD_H): Test whether isatty is declared.
(gl_UNISTD_H_DEFAULTS): Initialize GNULIB_ISATTY, REPLACE_ISATTY.
* modules/unistd (Makefile.am): Substitute GNULIB_ISATTY,
REPLACE_ISATTY.
* modules/isatty: New file.
* doc/posix-functions/isatty.texi: Mention the new module.
Suggested by Paolo Bonzini.
