gccrs: expand: eager evaluate macros inside builtin macros

gccrs: expand: eager evaluate macros inside builtin macros

gcc/rust/ChangeLog:

	* ast/rust-ast.h (class MacroInvocData): Store expander as
	member of the class.
	(class Expr): Add `is_literal` virtual method
	* ast/rust-expr.h: Override `is_literal` for `LiteralExpr`s.
	* expand/rust-macro-builtins.cc (try_expand_macro_expression): New function.
	(try_extract_string_literal_from_fragment): Likewise.
	(try_expand_single_string_literal): Likewise.
	(try_expand_many_expr): Likewise.
	(parse_single_string_literal): Add macro expander as argument.
	(MacroBuiltin::include_bytes): Pass expander as argument to
	`parse_single_string_literal`.
	(MacroBuiltin::include_str): Likewise.
	(MacroBuiltin::compile_error): Likewise.
	(MacroBuiltin::include): Likewise.
	(MacroBuiltin::concat): Likewise and add better error handling.
	(MacroBuiltin::env): Likewise.
	* expand/rust-macro-expand.cc (MacroExpander::expand_invoc): Expand
	invocations recursively.

gcc/testsuite/ChangeLog:

	* rust/compile/builtin_macro_concat.rs: Fix test error messages.
	* rust/compile/builtin_macro_env.rs: Likewise.

Signed-off-by: Zixing Liu <liushuyu011@gmail.com>