Implement X11 onscreen framerate counter.

This FPS counter is disabled by default.

Change-Id: Ida04352dece25a212cb678c9ceca4c31d654f373
Reviewed-on: https://swiftshader-review.googlesource.com/12128
Tested-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
diff --git a/src/Main/libX11.cpp b/src/Main/libX11.cpp
index 9c056bf..f3723ff 100644
--- a/src/Main/libX11.cpp
+++ b/src/Main/libX11.cpp
@@ -35,6 +35,7 @@
 	XCreateImage = (XImage *(*)(Display*, Visual*, unsigned int, int, int, char*, unsigned int, unsigned int, int, int))getProcAddress(libX11, "XCreateImage");
 	XCloseDisplay = (int (*)(Display*))getProcAddress(libX11, "XCloseDisplay");
 	XPutImage = (int (*)(Display*, Drawable, GC, XImage*, int, int, int, int, unsigned int, unsigned int))getProcAddress(libX11, "XPutImage");
+	XDrawString = (int (*)(Display*, Drawable, GC, int, int, char*, int))getProcAddress(libX11, "XDrawString");
 
 	XShmQueryExtension = (Bool (*)(Display*))getProcAddress(libXext, "XShmQueryExtension");
 	XShmCreateImage = (XImage *(*)(Display*, Visual*, unsigned int, int, char*, XShmSegmentInfo*, unsigned int, unsigned int))getProcAddress(libXext, "XShmCreateImage");