[gfortran, PR33269] Simplify FORMAT expressions before checking them

[Tobias Schlüter]

Hi,

this patch is completely straightforward: call gfc_simplify_expr() on 
the format string before checking its validity via 
check_format_string().  This is done during resolutions, so the call to 
gfc_simplify_expr() doesn't happen unduly early.  I also moved some 
checks into check_format as they belonged there IMO.

Built and tested on i386-darwin with clean testsuite runs except for the 
known do_3.f90 failures and the ones I mentioned in my earlier mail.  Ok?

Cheers,
- Tobi