testsuite: prevent packing enum in vect-early-break_65.c [PR124112]

GCC might be compiled with -fshort-enum enabled by default.
For those targets, it is important that the enum type is not packed into
something smaller than int, or vectorization will not match.

gcc/testsuite/ChangeLog:

	PR testsuite/124112
	* gcc.dg/vect/vect-early-break_65.c: Prevent packing enum to a
	smaller object.

Signed-off-by: Torbjörn SVENSSON <torbjorn.svensson@foss.st.com>
(cherry picked from commit 7aa3a196148f8b35619f38020164d15e1eace7fb)