[bootstrap-O1] add initializers to avoid warnings at -O1

[bootstrap-O1] add initializers to avoid warnings at -O1

Building with the bootstrap-O1 configuration option fails to compile a
number of files due to AFAICT false-positive warnings about uses of
uninitialized variables.

This patch adds dummy initializers to silence them all.

for  gcc/ChangeLog

	* multiple_target.c (create_dispatcher_calls): Init e_next.
	* tree-ssa-loop-split.c (split_loop): Init border.
	* tree-vect-loop.c (vect_determine_vectorization_factor): Init
	scalar_type.

From-SVN: r244086