gccrs: Add containers for proc macro collection mappings

gccrs: Add containers for proc macro collection mappings

Add one container for each kind of procedural macro mapping. Also add a
new structure to gather informations required for derive procedural
macros. Add different functions to fill those new containers.

gcc/rust/ChangeLog:

	* backend/rust-compile-context.h (struct CustomDeriveInfo): Add
	new derive procedural macro metadata information holder for
	mappings.

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