...of code. Thanks to @MyAAC
PKG_CHECK_MODULES(LUA, lua5.1 >= 5.1, , [
AC_CHECK_HEADERS([lua.hpp], , [AC_MSG_ERROR("Lua header not found.")])
AC_CHECK_LIB(lua, main, , [AC_MSG_ERROR("Linking against Lua library failed.")])
])
PKG_CHECK_MODULES([LUA], [lua5.1]...