m4: Fix lua.hpp check to actually work

diff --git a/m4/pdns_check_lua_hpp.m4 b/m4/pdns_check_lua_hpp.m4
index 64a3acc9e8555fa0af9a093e0925352bcd8c122b..7cc8f5e8f6d2f44f17057eee789a3489eb369927 100644 (file)
--- a/m4/pdns_check_lua_hpp.m4
+++ b/m4/pdns_check_lua_hpp.m4
@@ -1,7 +1,10 @@
 AC_DEFUN([PDNS_CHECK_LUA_HPP],[
   AC_REQUIRE([PDNS_WITH_LUA])
   AS_IF([test "x$LUAPC" != "x" ], [
+    OLD_CPPFLAGS="$CPPFLAGS"
+    CPPFLAGS="$CPPFLAGS $LUA_CFLAGS"
     AC_CHECK_HEADER([lua.hpp], [ have_lua_hpp=y ])
+    CPPFLAGS="$OLD_CPPFLAGS"
   ])
   AM_CONDITIONAL([HAVE_LUA_HPP], [ test x"$have_lua_hpp" = "xy" ])
 ])