Fix Windows build.

Take 2. Probably should have done this in the beginning, but thought I was
being clever.

Change-Id: I85c6e487eece9bcc75f8f62c850c2d4d1ee9e908

include/utils/file.h

@@ -24,8 +24,11 @@ namespace android {
 
 bool ReadFileToString(const std::string& path, std::string* content);
 bool WriteStringToFile(const std::string& content, const std::string& path);
+
+#if !defined(_WIN32)
 bool WriteStringToFile(const std::string& content, const std::string& path,
                        mode_t mode, uid_t owner, gid_t group);
+#endif
 
 } // namespace android