Fix build issues on Linux

panda/src/display/Sources.pp

@@ -107,7 +107,7 @@
   // link with it in direct/src/plugin, without pulling in the rest of
   // Panda.
 
-  #define BUILD_TARGET $[and $[OSX_PLATFORM],$[HAVE_P3D_PLUGIN]]
+  #define BUILD_TARGET $[and $[or $[OSX_PLATFORM],$[UNIX_PLATFORM]],$[HAVE_P3D_PLUGIN]]
 
   #define TARGET subprocbuffer
 

panda/src/display/subprocessWindowBuffer.cxx

@@ -15,6 +15,7 @@
 #include "subprocessWindowBuffer.h"
 #include <sys/mman.h>
 #include <fcntl.h>
+#include <string.h>
 
 #include <iostream>
 using namespace std;