make gc branch compile on Win32.

src/compiler-intrinsics.h

Index: src/compiler-intrinsics.h
diff --git a/src/compiler-intrinsics.h b/src/compiler-intrinsics.h
index bce5d56e25ef91a2b8af5dcf6b68e0596548609e..79ddac8720664af9986e441c177068955e7ddd04 100644
--- a/src/compiler-intrinsics.h
+++ b/src/compiler-intrinsics.h
@@ -50,6 +50,24 @@ int CompilerIntrinsics::CountTrailingZeros(uint32_t value) {
 int CompilerIntrinsics::CountLeadingZeros(uint32_t value) {
   return __builtin_clz(value);
 }
+
+#elif defined(_MSC_VER)
+
+#pragma intrinsic(_BitScanForward)
+#pragma intrinsic(_BitScanReverse)
+
+int CompilerIntrinsics::CountTrailingZeros(uint32_t value) {
+  unsigned long result;
+  _BitScanForward(&result, static_cast<long>(value));
+  return static_cast<int>(result);
+}
+
+int CompilerIntrinsics::CountLeadingZeros(uint32_t value) {
+  unsigned long result;
+  _BitScanReverse(&result, static_cast<long>(value));
+  return 31 - static_cast<int>(result);
+}
+
 #else
 #error Unsupported compiler
 #endif