isatty: Make it return true in Cygwin consoles on native Windows. * lib/isatty.c: Include <string.h>. (GetProcAddress): New macro. (GetNamedPipeClientProcessIdFuncType): New type. (GetNamedPipeClientProcessIdFunc): New variable. (QueryFullProcessImageNameFuncType): New type. (QueryFullProcessImageNameFunc): New variable. (initialized): New variable. (initialize): New function. (IsCygwinConsoleHandle): New function. (isatty): Invoke it. * doc/posix-functions/isatty.texi: Mention the issue.

#!/bin/sh

st=0
for i in 0 1 2 3 4 5 6 7 ; do
  ${CHECKER} ./test-spawn-pipe-main${EXEEXT} ./test-spawn-pipe-child${EXEEXT} $i \
    || { echo test-spawn-pipe.sh: iteration $i failed >&2; st=1; }
done
exit $st