quad_math: fix or suppress cppcheck warnings

sys/quad_math/muldi3.c

@@ -97,7 +97,7 @@ quad_t __muldi3(quad_t a, quad_t b)
 {
     union uu u, v, low, prod;
     u_int high, mid, udiff, vdiff;
-    int negall, negmid;
+    int negall;
 #define u1  u.ul[H]
 #define u0  u.ul[L]
 #define v1  v.ul[H]
@@ -131,6 +131,7 @@ quad_t __muldi3(quad_t a, quad_t b)
         prod.q = __lmulq(u0, v0);
     }
     else {
+        int negmid;
         /*
          * Compute the three intermediate products, remembering
          * whether the middle term is negative.  We can discard

sys/quad_math/qdivrem.c

@@ -78,6 +78,8 @@ __qdivrem(u_quad_t uq, u_quad_t vq, u_quad_t *arq)
         /* divide by zero. */
         static volatile const unsigned int zero = 0;
 
+        /* cppcheck-suppress zerodiv
+         * Divission by zero is on purpose here */
         tmp.ul[H] = tmp.ul[L] = 1 / zero;
 
         if (arq) {