dup2() dumps core on corner case

[Eric Blake <eblake at redhat dot com>]

Detected by gnulib's unit tests.  STC:

$ cat foo.c
#include <unistd.h>
int main() {
  return dup2(0, -1);
}
$ gcc -o foo -g -Wall foo.c
$ ./foo
Segmentation fault (core dumped)

cygwin 1.7.17-1

Running under gdb shows:
      4 [main] foo 1220 exception::handle: Exception:
STATUS_ACCESS_VIOLATION
    702 [main] foo 1220 open_stackdumpfile: Dumping stack trace to
foo.exe.stackdump

Program received signal SIGSEGV, Segmentation fault.
0x610e9407 in dup2 () from /usr/bin/cygwin1.dll

Expected results should be a normal failure with EBADF in errno.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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