Fix Win64 build of Dart VM.

runtime/bin/platform_win.cc

Index: runtime/bin/platform_win.cc
diff --git a/runtime/bin/platform_win.cc b/runtime/bin/platform_win.cc
index 85b6694d47dba42a51d60eb42c083047b95ec09f..0d3cb11c2f15306bf94199380fa46d69e509e80d 100644
--- a/runtime/bin/platform_win.cc
+++ b/runtime/bin/platform_win.cc
@@ -59,8 +59,10 @@ char** Platform::Environment(intptr_t* count) {
 }
 
 
-void Platform::FreeEnvironment(char** env, int count) {
-  for (int i = 0; i < count; i++) free(env[i]);
+void Platform::FreeEnvironment(char** env, intptr_t count) {
+  for (intptr_t i = 0; i < count; i++) {
+    free(env[i]);
+  }
   delete[] env;
 }