gccrs: early-name-resolver: Add simple macro name resolution

gccrs: early-name-resolver: Add simple macro name resolution

This name resolver performs the same macro name resolution as what was
previously done by the AttrVisitor visitor and macro expander.

It also resolves macro expressions in builtin-macros properly, as well
as expanded AST nodes when necessary.

gcc/rust/ChangeLog:

	* Make-lang.in: Compile early name resolver.
	* expand/rust-attribute-visitor.cc (AttrVisitor::visit): Move macro
	name resolution.
	* expand/rust-macro-builtins.cc (try_expand_macro_expression): Run ENR
	when recursively expanding macros.
	* expand/rust-macro-expand.cc (MacroExpander::expand_invoc): No longer
	perform name resolution in `expand_invoc`.
	* expand/rust-macro-expand.h (struct MacroExpander): Keep ENR within
	MacroExpander.
	* rust-session-manager.cc (Session::expansion): Run ENR.
	* resolve/rust-early-name-resolver.cc: New file.
	* resolve/rust-early-name-resolver.h: New file.