Revert "Remove support for MSVC"

sky/engine/wtf/BitwiseOperations.h

Index: sky/engine/wtf/BitwiseOperations.h
diff --git a/sky/engine/wtf/BitwiseOperations.h b/sky/engine/wtf/BitwiseOperations.h
index 41c14acde04338fc8d8990d24aa2e161fd25649e..4808efeda69644639885964bba564a44a2477001 100644
--- a/sky/engine/wtf/BitwiseOperations.h
+++ b/sky/engine/wtf/BitwiseOperations.h
@@ -42,9 +42,32 @@
 
 #include <stdint.h>
 
+#if COMPILER(MSVC)
+#include <intrin.h>
+#endif
+
 namespace WTF {
 
-#if COMPILER(GCC)
+#if COMPILER(MSVC)
+
+ALWAYS_INLINE uint32_t countLeadingZeros32(uint32_t x)
+{
+    unsigned long index;
+    return LIKELY(_BitScanReverse(&index, x)) ? (31 - index) : 32;
+}
+
+#if CPU(64BIT)
+
+// MSVC only supplies _BitScanForward64 when building for a 64-bit target.
+ALWAYS_INLINE uint64_t countLeadingZeros64(uint64_t x)
+{
+    unsigned long index;
+    return LIKELY(_BitScanReverse64(&index, x)) ? (63 - index) : 64;
+}
+
+#endif
+
+#elif COMPILER(GCC)
 
 // This is very annoying. __builtin_clz has undefined behaviour for an input of
 // 0, even though these's clearly a return value that makes sense, and even