tools: selftests: riscv: Add missing include for vector test

GCC raises the following warning:
  warning: 'status' may be used uninitialized
The warning comes from the fact, that the signature of waitpid() is
unknown and therefore the initialization of GCC cannot be guessed.
Let's add the relevant header to address this warning.

Signed-off-by: Christoph Müllner <[email protected]>
Reviewed-by: Alexandre Ghiti <[email protected]>
Reviewed-by: Andy Chiu <[email protected]>
Reviewed-by: Andrew Jones <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Palmer Dabbelt <[email protected]>

Author: cmuellner

tools/testing/selftests/riscv/vector/vstate_exec_nolibc.c

@@ -1,4 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0-only
+
+#include <linux/wait.h>
+
 #define THIS_PROGRAM "./vstate_exec_nolibc"
 
 int main(int argc, char **argv)