gccrs: Collect procedural macros in the crate

gccrs: Collect procedural macros in the crate

Collect informations on procedural macros in the compiled crate. For
attribute and bang procedural macros we only require the final address
as well as the name of the function. Derive procedural macros are a bit
different, we collect the fonction's address through it's fndecl tree as
well as the trait's name and the multiple attributes.

gcc/rust/ChangeLog:

	* backend/rust-compile-base.cc (HIRCompileBase::setup_fndecl):
	Make the function non static in order to be able to access the
	compile context. Also add the whole proc macro infomrmation
	collection.
	(get_attributes): Add a function to retrieve the different
	attributes from a derive procedural macro definition attribute.
	(get_trait_name): Add a function to retrieve the trait name from
	a derive procedural macro definition attribute.
	* backend/rust-compile-base.h: Add function prototypes.

Signed-off-by: Pierre-Emmanuel Patry <pierre-emmanuel.patry@embecosm.com>