FEXRootFSFetcher: Update and fix xxhash file hashing

The final tail of the file reading was incorrect, so our hashing was
"correct" but it was using stale data from the previous block size read.

Noticed this while wiring up the CI rootfs fetching since the hashing is
a lot simpler there.

Now instead of reading a tail, just attempt to read the full block size
and use the resulting data size instead. Confirmed it matches expected
results now.

In the process we are going to need to update hyperlinks and hashes
anyway, change the hash to XXH3 so it is faster to run.

Source/Tools/FEXRootFSFetcher/XXFileHash.cpp

@@ -28,32 +28,31 @@ namespace XXFileHash {
     lseek(fd, 0, SEEK_SET);
 
     // Set up XXHash state
-    XXH64_state_t* const State = XXH64_createState();
+    XXH3_state_t* const State = XXH3_createState();
     XXH64_hash_t const Seed = 0;
 
     if (!State) {
       return HadError();
     }
 
-    if (XXH64_reset(State, Seed) == XXH_ERROR) {
+    if (XXH3_64bits_reset_withSeed(State, Seed) == XXH_ERROR) {
       return HadError();
     }
 
     std::vector<char> Data(BLOCK_SIZE);
-    off_t DataRemaining = Size - BLOCK_SIZE;
-    off_t DataTail = Size - DataRemaining;
     off_t CurrentOffset = 0;
     auto Now = std::chrono::high_resolution_clock::now();
 
     // Let the kernel know that we will be reading linearly
     posix_fadvise(fd, 0, Size, POSIX_FADV_SEQUENTIAL);
-    while (CurrentOffset < DataRemaining) {
+    while (CurrentOffset < Size) {
+
       ssize_t Result = pread(fd, Data.data(), BLOCK_SIZE, CurrentOffset);
       if (Result == -1) {
         return HadError();
       }
 
-      if (XXH64_update(State, Data.data(), BLOCK_SIZE) == XXH_ERROR) {
+      if (XXH3_64bits_update(State, Data.data(), Result) == XXH_ERROR) {
         return HadError();
       }
       auto Cur = std::chrono::high_resolution_clock::now();
@@ -62,21 +61,11 @@ namespace XXFileHash {
         fmt::print("{}% hashed\n", (double)CurrentOffset / SizeD);
         Now = Cur;
       }
-      CurrentOffset += BLOCK_SIZE;
+      CurrentOffset += Result;
     }
 
-    // Finish the tail
-    ssize_t Result = pread(fd, Data.data(), DataTail, CurrentOffset);
-    if (Result == -1) {
-      return HadError();
-    }
-
-    if (XXH64_update(State, Data.data(), DataTail) == XXH_ERROR) {
-      return HadError();
-    }
-
-    XXH64_hash_t const Hash = XXH64_digest(State);
-    XXH64_freeState(State);
+    XXH64_hash_t const Hash = XXH3_64bits_digest(State);
+    XXH3_freeState(State);
 
     close(fd);
     return {true, Hash};