[gfortran] Add a global symbol table

[Paul Brook]

> This is achieved by keeping a table of global symbols. A possible future
> application for this might be checking if external subroutines are
> called with consistent argument list. Additionally, the disallowed case
> of two empty BLOCK DATA is caught.

We already have a global namespace for intrinsic subroutines. See 
gfc_intrinsic_namespace in intrinsic.c.
Could/Should this be be merged with your proposal? 

> 2004-06-25  Tobias Schlueter  <tobias.schlueter@physik.uni-muenchen.de>
> 	Andrew Vaught  <andyv@firstinter.net>
>
> 	* gfortran.h (gfc_gsymbol): New typedef.
> 	(gfc_gsym_root): New variable.
> 	(gfc_get_gsymbol, gfc_find_gsym): New prototypes.
> 	* parse.c (global_used): New function.
> 	(parse_block_data): Check for double empty BLOCK DATA,
> 	use global symbol table.
> 	(parse_module): Use global symbol table.
> 	(add_global_procedure, add_global_program): New functions.
> 	(gfc_parse_file): Use global symbol table.
> 	* symbol.c (gfc_gsym_root): New variable.
> 	(gfc_find_gsym, gsym_compare, gfc_get_gsymbol): New
> 	functions.

Ok, after you've considered the comments above and decided you still want to 
do it this way.

Paul