c-common.c (c_common_truthvalue_conversion): Warn if the address of a non-weak function is used as a truth value.

gcc/
	* c-common.c (c_common_truthvalue_conversion): Warn if the
	address of a non-weak function is used as a truth value.

cp/
	* cvt.c (ocp_convert): Move warning to C common code.

testsuite/
	* gcc.dg/weak/weak-3.c: Fix for new warning.

From-SVN: r72409