gccrs: Add Debug info testsuite

This testsuite is specifically about testcases which scan the asm debug
info for results.

	gcc/testsuite/
	* rust/debug/chartype.rs: New.
	* rust/debug/custom_link_section.rs: New.
	* rust/debug/debug.exp: New.
	* rust/debug/i8u8.rs: New.
	* rust/debug/lang.rs: New.
	* rust/debug/no_mangle.rs: New.
	* rust/debug/oldlang.rs: New.
	* rust/debug/tuple.rs: New.
	* rust/debug/win64-abi.rs: New.

Co-authored-by: Tom Tromey <tom@tromey.com>
Co-authored-by: Mark Wielaard <mark@klomp.org>
Co-authored-by: Marc Poulhiès <dkm@kataplop.net>