jit: fix segfault with autovectorization (PR tree-optimization/46805)

jit: fix segfault with autovectorization (PR tree-optimization/46805)

libgccjit ran into its own version of PR tree-optimization/46805 (seen
with the Go frontend); this patch fixes it in the same way.

gcc/jit/ChangeLog:
	PR tree-optimization/46805
	* dummy-frontend.c (jit_langhook_parse_file): Handle vector types.

gcc/testsuite/ChangeLog:
	PR tree-optimization/46805
	* jit.dg/all-non-failing-tests.h: Add test-autovectorize.c.
	* jit.dg/test-autovectorize.c: New test case.

From-SVN: r251192