gccrs: Fix duplicated function generation on higher ranked trait bounds

gccrs: Fix duplicated function generation on higher ranked trait bounds

Deuplicate function elimination can fail when we compile helpers during
higher ranked trait bound monomorphization. This because the
TyTy::BaseType info can be lost/reset during the compilation process. This
adds a second mechanism to match based on the manged names which is a bit
more reliable. This patch is required since the query based refactor of
the type system so this issue was likely hidden to to using duplicated type
info for higher ranked trait bounds.

gcc/rust/ChangeLog:

	* backend/rust-compile-context.h: Add new optional `asm_name` string
	argument to `lookup_function_decl`.
	* backend/rust-compile-item.cc (CompileItem::visit): Compute assembly
	name and pass it to `lookup_function_decl` when calling it.