[PATCH,fortran]: fix bind(c) common block alignment

[François-Xavier Coudert]

> if it is acceptable for all common blocks to choose a C compatible
> alignment, then the patch is trivial to change to do this.  is that what
> people prefer?

I think we certainly do not want to rush that decision. I bit of
investigation, seeing what g77 did, what other compilers do, etc. is
certainly necessary before changing an established behaviour.

FX