jit: Add new testcase missing from r218521

I intended for r218521 to contain this file:

gcc/testsuite/ChangeLog:
	* jit.dg/test-error-unrecognized-dump.c: New file.

Add it.

From-SVN: r218522

gcc/testsuite/jit.dg/test-error-unrecognized-dump.c

+#include <stdlib.h>
+#include <stdio.h>
+
+#include "libgccjit.h"
+
+#include "harness.h"
+
+static char *dump;
+
+void
+create_code (gcc_jit_context *ctxt, void *user_data)
+{
+  gcc_jit_context_enable_dump (ctxt,
+			       "not-a-valid-dump-switch",
+			       &dump);
+}
+
+void
+verify_code (gcc_jit_context *ctxt, gcc_jit_result *result)
+{
+  CHECK_VALUE (result, NULL);
+
+  /* Verify that the correct error message was emitted.  */
+  CHECK_STRING_VALUE (gcc_jit_context_get_first_error (ctxt),
+		      "unrecognized dump: not-a-valid-dump-switch");
+}
+