gccrs: Improve method resolution to use seperate indexes for impl's

gcc/rust/ChangeLog:

	* typecheck/rust-hir-dot-operator.cc (MethodResolver::select): use sperate index
	* util/rust-hir-map.cc (Mappings::insert_hir_impl_block): new indexes
	* util/rust-hir-map.h: likewise

Signed-off-by: Philip Herron <herron.philip@googlemail.com>
3 files changed