Add a simple /bin/sysctl that wraps the files in /proc/sys.

AK/StringBuilder.cpp

@@ -40,12 +40,14 @@ void StringBuilder::appendf(const char* fmt, ...)
 ByteBuffer StringBuilder::to_byte_buffer()
 {
     m_buffer.trim(m_length);
-    return m_buffer;
+    return move(m_buffer);
 }
 
 String StringBuilder::build()
 {
-    return String((const char*)m_buffer.pointer(), m_length);
+    auto string = String((const char*)m_buffer.pointer(), m_length);
+    m_buffer.clear();
+    return string;
 }
 
 }