Made SDL 2 m4 script check for presence of macro provided by pkg-config to avoid an error when pkg-config is not installed.
Made SDL 2 m4 script check for presence of macro provided by pkg-config to avoid an error when pkg-config is not installed.

adamsdadakaeti/bzflag,adamsdadakaeti/bzflag,kongr45gpen/bzflag,adamsdadakaeti/bzflag,adamsdadakaeti/bzflag,khonkhortisan/bzflag,khonkhortisan/bzflag,kongr45gpen/bzflag,kongr45gpen/bzflag,kongr45gpen/bzflag,khonkhortisan/bzflag,kongr45gpen/bzflag,kongr45gpen/bzflag,kongr45gpen/bzflag,adamsdadakaeti/bzflag,khonkhortisan/bzflag,khonkhortisan/bzflag,khonkhortisan/bzflag,adamsdadakaeti/bzflag,adamsdadakaeti/bzflag,kongr45gpen/bzflag,khonkhortisan/bzflag