Comment # 4 on bug 1226307 from Gordon Leung

Turns out the luajit headers ARE included in luajit-devel just in a
(non-standard) directory which is: /usr/include/luajit-5_1-2.1

So any package which wants to build with luajit-devel headers needs to add:
export LUA_INCLUDE="-I/usr/include/luajit-5_1-2.1"
to their %build and %install sections.