zlib: Remove Windows XP workaround for CPU feature detection

third_party/zlib/x86.c

 /*
  * x86 feature check
  *
  * Copyright (C) 2013 Intel Corporation. All rights reserved.
  * Author:
  *  Jim Kukunas
  * 
  * For conditions of distribution and use, see copyright notice in zlib.h
  */
 
@@ skipping 38 matching lines @@
     x86_cpu_has_sse42 = ecx & 0x100000;
     x86_cpu_has_pclmulqdq = ecx & 0x2;
 
     x86_cpu_enable_simd = x86_cpu_has_sse2 &&
                           x86_cpu_has_sse42 &&
                           x86_cpu_has_pclmulqdq;
 }
 #else
 #include <intrin.h>
 #include <windows.h>
-#include <stdint.h>
 
-static volatile int32_t once_control = 0;
-static void _x86_check_features(void);
-static int fake_pthread_once(volatile int32_t *once_control,
-                             void (*init_routine)(void));
+static BOOL CALLBACK _x86_check_features(PINIT_ONCE once,
+                                         PVOID param,
+                                         PVOID *context);
+static INIT_ONCE cpu_check_inited_once = INIT_ONCE_STATIC_INIT;
 
 void x86_check_features(void)
 {
-    fake_pthread_once(&once_control, _x86_check_features);
+    InitOnceExecuteOnce(&cpu_check_inited_once, _x86_check_features,
+                        NULL, NULL);
 }
 
-/* Copied from "perftools_pthread_once" in tcmalloc */
-static int fake_pthread_once(volatile int32_t *once_control,
-                             void (*init_routine)(void)) {
-    // Try for a fast path first. Note: this should be an acquire semantics read
-    // It is on x86 and x64, where Windows runs.
-    if (*once_control != 1) {
-        while (1) {
-            switch (InterlockedCompareExchange(once_control, 2, 0)) {
-                case 0:
-                    init_routine();
-                    InterlockedExchange(once_control, 1);
-                    return 0;
-                case 1:
-                    // The initializer has already been executed
-                    return 0;
-                default:
-                    // The initializer is being processed by another thread
-                    SwitchToThread();
-            }
-        }
-    }
-    return 0;
-}
-
-static void _x86_check_features(void)
+static BOOL CALLBACK _x86_check_features(PINIT_ONCE once,
+                                         PVOID param,
+                                         PVOID *context)
 {
     int x86_cpu_has_sse2;
     int x86_cpu_has_sse42;
     int x86_cpu_has_pclmulqdq;
     int regs[4];
 
     __cpuid(regs, 1);
 
     x86_cpu_has_sse2 = regs[3] & 0x4000000;
     x86_cpu_has_sse42= regs[2] & 0x100000;
     x86_cpu_has_pclmulqdq = regs[2] & 0x2;
 
     x86_cpu_enable_simd = x86_cpu_has_sse2 &&
                           x86_cpu_has_sse42 &&
                           x86_cpu_has_pclmulqdq;
+    return TRUE;
 }
 #endif  /* _MSC_VER */