Fix check for pthreads.h pollution on Mingw64
A previous commit attempted to workaround pollution in the
Mingw64 pthreads.h header file
commit
d5fec6c22f03c6a73d62260c9ce091c10c0a9cbd
Author: Eric Blake <eblake@redhat.com>
Date: Wed Jan 22 20:39:45 2014 -0700
pthread: work around winpthread header pollution on mingw
It activated its workaround based on existance of the strtok_r
wrapper in pthreads.h. As luck would have it, latest Mingw64
headers removed the strtok_r wrapper from pthreads.h, but left
all the others. So the gnulib workaround was not activated.
Change the configure check to look for several of the broken
wrappers, instead of just strtok_r
Signed-off-by: Eric Blake <eblake@redhat.com>