[runtime] Fixed UB with signed overflow

kotlin-native/runtime/src/main/cpp/polyhash/arm.cpp

@@ -99,7 +99,7 @@ int polyHash_arm(int length, uint16_t const* str) {
         // Vectorization is not supported.
         return polyHash_naive(length, str);
     }
-    int res;
+    uint32_t res;
     if (length < 488)
         res = NeonTraits::polyHashUnalignedUnrollUpTo16(length / 4, str);
     else

kotlin-native/runtime/src/main/cpp/polyhash/naive.h

@@ -9,7 +9,7 @@
 #include <cstdint>
 
 inline int polyHash_naive(int length, uint16_t const* str) {
-    int res = 0;
+    uint32_t res = 0;
     for (int i = 0; i < length; ++i)
         res = res * 31 + str[i];
     return res;

kotlin-native/runtime/src/main/cpp/polyhash/x86.cpp

@@ -143,7 +143,7 @@ int polyHash_x86(int length, uint16_t const* str) {
         // Either vectorization is not supported or the string is too short to gain from it.
         return polyHash_naive(length, str);
     }
-    int res;
+    uint32_t res;
     if (length < 32)
         res = SSETraits::polyHashUnalignedUnrollUpTo8(length / 4, str);
     else if (!avx2Supported)