PR modula2/109102 Wrong quotes in diagnostic

The backtick and single quote should be replaced with %< and %> or
%qs.

gcc/m2/ChangeLog:

	PR modula2/109102
	* gm2-gcc/m2builtins.cc (ASSERT): Change format specifier to
	use %qs rather than quotes.

Signed-off-by: Gaius Mulley <gaiusmod2@gmail.com>