[patchv2+7.9] compile: Filter out -fpreprocessed

[Joel Brobecker]

> gdb/ChangeLog
> 2015-01-17  Jan Kratochvil  <jan.kratochvil@redhat.com>
> 
> 	Filter out inferior gcc option -fpreprocessed.
> 	* compile/compile.c (filter_args): New function.
> 	(get_args): Use it.

Looks good to me; and OK for both master and branch.

Thank you,
-- 
Joel