zip_archive.cc: fix ubsan false positive

std::hash returns a 64 bit value, which is truncated to a 32 bit value
in ComputeHash. ubsan's implicit-unsigned-integer-truncation doesn't
like this implicit truncation and crashes the program. Explicitly strip
off the top order bits after computing the hash.

Remove the windows specific version of the hash computation. The windows
compile now uses clang, so this code is obsolete. This also avoids us
having to add __attribute__((no_sanitize("integer"))) to the windows
code.

This is needed to support Android booting with ubsan's
implicit-unsigned-integer-truncation option enabled.

Test: compiles and boots
Bug: 122975762
Change-Id: I2f05fbf5ffee8e90a66a6fda32e80de9cca246c0

libziparchive/zip_archive.cc

@@ -102,21 +102,9 @@ static uint32_t RoundUpPower2(uint32_t val) {
 }
 
 static uint32_t ComputeHash(const ZipString& name) {
-#if !defined(_WIN32)
   return std::hash<std::string_view>{}(
-      std::string_view(reinterpret_cast<const char*>(name.name), name.name_length));
-#else
-  // Remove this code path once the windows compiler knows how to compile the above statement.
-  uint32_t hash = 0;
-  uint16_t len = name.name_length;
-  const uint8_t* str = name.name;
-
-  while (len--) {
-    hash = hash * 31 + *str++;
-  }
-
-  return hash;
-#endif
+             std::string_view(reinterpret_cast<const char*>(name.name), name.name_length)) &
+         UINT32_MAX;
 }
 
 static bool isZipStringEqual(const uint8_t* start, const ZipString& zip_string,