emcc compile fails on openGL's symbol glLoadMatrixf

I am trying to compile agar, a widgets/GUI library that also works through SDL. When compiling a helloworld as follows:
```bash
emcc -I/home/kabira/opensourceforgery/libagar/include/agar/ helloworld.c -L/home/kabira/o
pensourceforgery/libagar/lib -lag_core -lag_gui
```
I get the undef reference error:
```
error: undefined symbol: glLoadMatrixf (referenced by top-level compiled C/C++ code)
```
I tried using various flags regardng ES2 and SDL but that doesn't work. Not sure what libraries to link against.