build_min_non_dep wasn't setting any location so when we were emitting the
warning in the following test while instantiating a template, its location
was UNKNOWN_LOCATION.  Rather than adding a location_t parameter, let's use
the location from the original expression.

	* tree.c (build_min_non_dep): Use the location of NON_DEP when
	building the expression.

	* g++.dg/diagnostic/enum1.C: New test.
	* g++.dg/gomp/loop-2.C: Adjust dg-error.
	* g++.dg/gomp/for-21.C: Likewise.

From-SVN: r279685