Using xxhash xxh_x86dispatch to select the best SIMD instruction set at runtime

This dispatcher can not be added in a unity build and we must remove
AVX2 or AVX512 compilation flags, link xxh_x86dispatch.c in the
compilation command. The compilaiton throws two warnings about function
with internal linkage but not defined, they are defined in
xxh_x86dispatch.c so it's harmless warnings

platform.h

@@ -7,12 +7,9 @@
 
 #include "arena.c"
 
-#define XXH_VECTOR                                                             \
-  XXH_AVX2 // not recommanded to compile with gcc see xxhash.h line 4082
-           // Must compile with /arch:AVX2 in clang-cl or -mavx2 in clang/gcc
+// xxhash include
 #define XXH_INLINE_ALL
-#include "xxhash.c"
-#include "xxhash.h"
+#include "xxh_x86dispatch.h"
 
 // ----------------------------- Config -------------------------------------
 #define FILE_HASHES_TXT "file_hashes.txt"
@@ -21,6 +18,15 @@
 #define READ_BLOCK (64 * 1024) // 64KB blocks
 
 // ----------------------------- Data types ---------------------------------
+// Timer
+typedef struct {
+  LARGE_INTEGER start;
+  LARGE_INTEGER end;
+} HiResTimer;
+
+static LARGE_INTEGER g_qpc_freq;
+
+// File entry
 typedef struct FileEntry {
   char *path;
 
@@ -30,31 +36,7 @@ typedef struct FileEntry {
   char owner[128];        // resolved owner name
 } FileEntry;
 
-void platform_get_file_times(const char *path, uint64_t *out_created,
-                             uint64_t *out_modified);
-void platform_get_file_owner(const char *path, char *out_owner,
-                             size_t out_owner_size);
-
-/* scan folder timer*/
-typedef struct {
-  LARGE_INTEGER start;
-  LARGE_INTEGER end;
-} HiResTimer;
-
-static LARGE_INTEGER g_qpc_freq;
-
-static void timer_init(void) { QueryPerformanceFrequency(&g_qpc_freq); }
-
-static void timer_start(HiResTimer *t) { QueryPerformanceCounter(&t->start); }
-
-static double timer_stop(HiResTimer *t) {
-  QueryPerformanceCounter(&t->end);
-  return (double)(t->end.QuadPart - t->start.QuadPart) /
-         (double)g_qpc_freq.QuadPart;
-}
-
-// Workers context
-
+// Threads context
 typedef struct {
   u8 num_threads;