[patch, fortran] Fix PR 84394

[Thomas Koenig]

Hello world,

this patch fixes a rejects-valid 7/8/9 regression where subroutines like
_deallocate are added to a derived type in a block data, and because
they were marked PRIVATE, an error occurred.

This solution is look for this particular case by checking for an
underscore as the first letter of the subroutine name.  This can only
occur for compiler-generated subroutines, so this should be safe.
I have also restricted this to the particular case of a BLOCK DATA
as not to mask other potential errors.

This is not elegant, but effecive...

Regression-tested.

Ok for trunk and backport?

Regards

	Thomas