Okay, try 2:
open configure.ac and find these lines:
#check lua 5.1
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 failed.")])
])
AC_SUBST(LUA_CFLAGS)...