add missing include to a_quake.cpp.

The GCC AppImage build reported

/usr/bin/ld: CMakeFiles/zdoom.dir/playsim/mapthinkers/a_quake.cpp.o: in function `AActor::Distance2D(AActor*, bool) const':
a_quake.cpp:(.text._ZNK6AActor10Distance2DEPS_b[_ZNK6AActor10Distance2DEPS_b]+0x2c): undefined reference to `AActor::PosRelative(AActor const*) const'

src/playsim/mapthinkers/a_quake.cpp

@@ -33,6 +33,7 @@
 #include "d_player.h"
 #include "r_utility.h"
 #include "g_levellocals.h"
+#include "actorinlines.h"
 #include <p_maputl.h>
 
 static FRandom pr_quake ("Quake");