gccrs: Fix duplicate "trailing semicolon in macro used" warnings

gcc/rust/ChangeLog:

	* expand/rust-macro-expand.cc (transcribe_expression (Parser<MacroInvocLexer>)):
	Prevent the same trailing semicolon warning from being generated at the same loc.

Signed-Off-By: Yap Zhi Heng <yapzhhg@gmail.com>