runtime: fix a UBSAN issue

This was identified by UBSAN: signed-integer-overflow.  Explicitly mark
the value as unsigned to ensure that the value does not overflow.  There
is a second instance of a raw literal, however, because it is a `*=` the
value is implicitly understood to be unsigned.

Author: compnerd

stdlib/public/runtime/MetadataCache.h

@@ -471,7 +471,7 @@ class MetadataCacheKey {
 
 private:
   uint32_t computeHash() const {
-    size_t H = 0x56ba80d1 * NumKeyParameters;
+    size_t H = 0x56ba80d1u * NumKeyParameters;
     for (unsigned index = 0; index != NumKeyParameters; ++index) {
       H = (H >> 10) | (H << ((sizeof(size_t) * 8) - 10));
       H ^= (reinterpret_cast<size_t>(Data[index])