[5/n] remove trapv-*.c special-casing of gcc.dg/vect/ files

The following makes -ftrapv explicit.

	* gcc.dg/vect/vect.exp: Remove special-casing of tests
	named trapv-*
	* gcc.dg/vect/trapv-vect-reduc-4.c: Add dg-additional-options -ftrapv.