compile:

$ clang -o hello  hello.c -lX11 -lGL -lGLEW -L/usr/X11/lib -I/opt/X11/include

Result:

+------------------------------------------+
|            Hello, World!        [_][~][X]|
+------------------------------------------+
|                                          |
|                   / \                    |
|                 /     \                  |
|               /         \                |
|             /             \              |
|           /                 \            |
|         /                     \          |
|       /                         \        |
|     /                             \      |
|    - - - - - - - - - - - - - - - - -     |
+------------------------------------------+