Build command fails on OpenBSD 6.5-release because it can't find `X11/Xlib.h`. One must specify the path to X11R6 as follows: C_INCLUDE_PATH="/usr/X11R6/include" LIBRARY_PATH="/usr/X11R6/lib" clang -Wno-parentheses -std=c11 -pedantic -D_DEFAULT_SOURCE oneko.c -o oneko -lc -lm -lX11 -lXext