Suppress MSAN detections in deflate's slide_hash().

slide_hash() knowingly reads potentially uninitialized memory, see
comment lower down about prev[n] potentially being garbage. In
this case, the result is never used.

deflate.c

@@ -179,6 +179,11 @@ local const config configuration_table[10] = {
  * bit values at the expense of memory usage). We slide even when level == 0 to
  * keep the hash table consistent if we switch back to level > 0 later.
  */
+#if defined(__has_feature)
+#  if __has_feature(memory_sanitizer)
+     __attribute__((no_sanitize("memory")))
+#  endif
+#endif
 local void slide_hash(deflate_state *s) {
     unsigned n, m;
     Posf *p;