#308 iconc: failure to compile c code: freetype2.h not found: workaround

[Charles Evans]

iconc would not build cobench.icn:

iconc cobench.icn
Translating to C:
cobench.icn:
No errors; no warnings
Compiling and linking C code:
In file included from cobench.h:8,
from cobench.c:12:
/home/ubuntu-budgie/temp/uni/unicon/rt/include/rt.h:3074:13: fatal error: ft2build.h: No such file or directory
3074 | #include <ft2build.h>
| ^~~~~~~~~~~~
compilation terminated.
C compile and link failed </ft2build.h>

workaround:
export C_INCLUDE_PATH=/usr/include/freetype2/