I cloned your charming repository and just ran make, and got an error.
Log is below.
% git clone https://github.com/takubo/awkGL.git
Cloning into 'awkGL'...
remote: Counting objects: 105, done.
remote: Compressing objects: 100% (39/39), done.
remote: Total 105 (delta 64), reused 105 (delta 64)
Receiving objects: 100% (105/105), 30.34 KiB, done.
Resolving deltas: 100% (64/64), done.
% cd awkGL
awkgl.c draggable_circle.awk earth_anti_alias.awk earth.awk earth_ez.awk earth_light.awk makefile planets.awk README.md sol_system.txt
gcc awkgl.c -Wall -fPIC -shared -c -O2 -DHAVE_STRING_H -DHAVE_SNPRINTF -DHAVE_STDARG_H -DHAVE_VPRINTF -DDYNAMIC -I/home/iorivur/gawk-4.0.1 -DHAVE_FREEGLUT
awkgl.c:9:17: fatal error: awk.h: No such file or directory
make: *** [awkgl.so] Error
Thank you for having interest in awkGL!
I show you how to succeed building awkGL.
First, download the source of gawk-4.0.1 from the following web site, and extract it.
The directory which has appeared includes awk.h.
Next, edit the 3rd line of makefile of awkGL as necessary.
AWK_H_DIR, in this line, must indicate the source directry of gawk-4.0.1.
And, try run make again.
Furthermore, awkGL run with gawk version 4.0.1.
If you do not have gawk 4.0.1, you need to build it, too.