write: Support for MSVC 9. * lib/unistd.in.h (write): Replace also when GNULIB_UNISTD_H_NONBLOCKING is not 1. * lib/write.c (write_nothrow): New function. (rpl_write): Define also when GNULIB_NONBLOCKING or GNULIB_SIGPIPE is not 1. Use write_nothrow. * m4/write.m4 (gl_FUNC_WRITE): Replace read if the platform has an invalid parameter handler. (gl_PREREQ_WRITE): New macro. * modules/write (Depends-on): Add msvc-inval. (configure.ac): Invoke gl_PREREQ_WRITE. * doc/posix-functions/write.texi: Mention the problem on MSVC.