random is not multithread-safe in Cygwin

[Bruno Haible]

Corinna Vinschen wrote:
> > And indeed glibc, musl libc, AIX, Android, and even NetBSD implement it in a
> > multithread-safe way.
> 
> Our code is from FreeBSD, originally.  I checked the latest code from
> FreeBSD.  It doesn't lock anything in random() and generates the same
> error when running the same test app.
> 
> Why is that ok for FreeBSD?

It is not OK in FreeBSD, either. This is what I noted in the Gnulib manual:
https://git.savannah.gnu.org/gitweb/?p=gnulib.git;a=blob;f=doc/posix-functions/random.texi

But it is MT-safe in NetBSD (in the '#ifndef SMALL_RANDOM' branch):
http://cvsweb.netbsd.org/bsdweb.cgi/src/common/lib/libc/stdlib/random.c?rev=1.7&content-type=text/x-cvsweb-markup

Bruno