Dear all,

when assigning character pointers, we have a check for same length,
which however does not trigger for character pointers within a
structure constructor.

The attached patch extends the character checks slightly to fix
this loophole.  I've verified that NAG and Crayftn behave similarly,
while Intel does not detect the length difference.

Regtested on x86_64-pc-linux-gnu.

OK for mainline?  Would it be still ok for 12, or rather wait until
branching for 13?

Thanks,
Harald