Dear Fortranners,

while we detect invalid uses of type(*), we may run into other issues
later when the declared variable is used, leading to an ICE due to a
NULL pointer dereference.  This is demonstrated by Gerhard's testcase.

Steve and I came to rather similar fixes, see PR.  Mine is attached.

Regtested on x86_64-pc-linux-gnu.  OK for mainline?

Thanks,
Harald