same fix for SS

SheepShaver/src/Unix/configure.ac

@@ -764,6 +764,9 @@ if [[ "x$WANT_SDL_VIDEO" = "xyes" ]]; then
     CPPFLAGS="$CPPFLAGS -I../MacOSX"
   else
     EXTRASYSSRCS="$EXTRASYSSRCS ../dummy/clip_dummy.cpp"
+    if [[ "$WANT_GTK" != "no" ]]; then
+      LIBS="$LIBS -lX11"
+    fi
   fi
 else
   VIDEOSRCS="video_x.cpp"

SheepShaver/src/Unix/main_unix.cpp

@@ -133,6 +133,7 @@
 
 #ifdef ENABLE_GTK
 #include <gtk/gtk.h>
+#include <X11/Xlib.h>
 #endif
 
 #ifdef ENABLE_XF86_DGA
@@ -728,6 +729,9 @@ static bool init_sdl()
 
 int main(int argc, char **argv)
 {
+#ifdef ENABLE_GTK
+	XInitThreads();
+#endif
 	char str[256];
 	bool memory_mapped_from_zero, ram_rom_areas_contiguous;
 	const char *vmdir = NULL;