1. install build dependencies:
$ tce-load -wi libX11-dev xorg-proto libXrandr-dev compiletc

2. per TC wiki, for maximum compatibility:
$ export CFLAGS="-mtune=generic -Os -pipe"
$ export CXXFLAGS="-mtune=generic -Os -pipe"
$ export LDFLAGS="-Wl,-O1"

3. 
$ gcc -o sct sct.c -lm -lX11 -lXrandr