gccrs: [E0617] attempt for invalid type variable in variadic function

gccrs: [E0617] attempt for invalid type variable in variadic function

There are some certain rust types must be cast before
passing them to a variadic function, because of arcane
ABI rules dictated by the C standard. To fix the error,
cast the value to the type specified by the error message.

gcc/rust/ChangeLog:

	* typecheck/rust-tyty-call.cc (TypeCheckCallExpr::visit):
	Added ErrorCode & more fixit hints.

gcc/testsuite/ChangeLog:

	* rust/compile/variadic.rs: Added new checks.

Signed-off-by: Muhammad Mahad <mahadtxt@gmail.com>