Implement correct OS and CC detection.

src/snapshot-common.cc

Index: src/snapshot-common.cc
diff --git a/src/snapshot-common.cc b/src/snapshot-common.cc
index 576269df9e442166fce92da22f54f6575ee1b842..b1a25d08e95cd86ea86541980f5580462bcfb113 100644
--- a/src/snapshot-common.cc
+++ b/src/snapshot-common.cc
@@ -47,7 +47,7 @@ static void ReserveSpaceForSnapshot(Deserializer* deserializer,
   CHECK_NE(NULL, fp);
   int new_size, pointer_size, data_size, code_size, map_size, cell_size,
       property_cell_size;
-#ifdef _MSC_VER
+#if V8_CC_MSVC
   // Avoid warning about unsafe fscanf from MSVC.
   // Please note that this is only fine if %c and %s are not being used.
 #define fscanf fscanf_s
@@ -59,7 +59,7 @@ static void ReserveSpaceForSnapshot(Deserializer* deserializer,
   CHECK_EQ(1, fscanf(fp, "map %d\n", &map_size));
   CHECK_EQ(1, fscanf(fp, "cell %d\n", &cell_size));
   CHECK_EQ(1, fscanf(fp, "property cell %d\n", &property_cell_size));
-#ifdef _MSC_VER
+#if V8_CC_MSVC
 #undef fscanf
 #endif
   fclose(fp);