Fix uncommon spawnpoints

[darkshade9]

Updated UncommonSpawnPoint() such that it will return the first valid spot it finds based on the array of entity string name matches in the map, starting with info_player_start. This only occurs if info_player_deathmatch or team related spawn entities are not found in the map (usually either non-AQ2 maps or unfinished ones). This also prints a warning in the console in case the author of the map is not aware.

This merge includes a change to meson.build that broke Windows builds, assuming that static: true is no longer a valid parameter for building libjpeg.

This merge also includes a few checks for the gl_shaders value and whether or not to use legacy GL commands.