Fixed NEON tests

libs/spandsp/m4/ax_check_arm_neon.m4

@@ -25,7 +25,16 @@ gnu)
         [AC_LANG_PROGRAM(
             [#include <arm_neon.h>
             int32x4_t testfunc(int16_t *a, int16_t *b)
-            {return vmull_s16(vld1_s16(a), vld1_s16(b));}],
+            {
+                return vmull_s16(vld1_s16(a), vld1_s16(b));
+            }
+            int main(int argc, char *argv[])
+            {
+                int32x4_t z;
+                int16_t x[8];
+                int16_t y[8];
+                z = testfunc(x, y);
+            }],
             [;]
         )],