publicize clockToMs function

Author: realSquidCoder

common.h

@@ -163,6 +163,9 @@ constexpr auto MAX_ANIMFRAME = 6;
 // binary 00111111
 constexpr auto ALL_FRAMES = 0b111111;
 
+//from Gui.cpp
+float clockToMs(float clockTicks);
+
 //from UserInput.cpp
 void doMouse();
 void doKeys(int32_t key, uint32_t keymod);