add unicode compatible file_lock for Windows

boost::interprocess::file_lock cannot open the files that contain characters which cannot be parsed by the user's code page on Windows.
This commit add a new class to handle those specific file for Windows.

src/fs.h

@@ -19,6 +19,26 @@ namespace fs = boost::filesystem;
 namespace fsbridge {
     FILE *fopen(const fs::path& p, const char *mode);
     FILE *freopen(const fs::path& p, const char *mode, FILE *stream);
+
+    class FileLock
+    {
+    public:
+        FileLock() = delete;
+        FileLock(const FileLock&) = delete;
+        FileLock(FileLock&&) = delete;
+        explicit FileLock(const fs::path& file);
+        ~FileLock();
+        bool TryLock();
+        std::string GetReason() { return reason; }
+
+    private:
+        std::string reason;
+#ifndef WIN32
+        int fd = -1;
+#else
+        void* hFile = (void*)-1; // INVALID_HANDLE_VALUE
+#endif
+    };
 };
 
 #endif // BITCOIN_FS_H