[client] added xlib-shim to disable calls to XSync

The compiled xlib-shim.so can be used to intercept and prevent SDL
from calling XSync, which causes latency issues on some video
hardware.

To use specify the full path to the file in the LD_PRELOAD
environment variable, like so:

LD_PRELOAD=/full/path/xlib-shim.so ./looking-glass

client/Makefile

@@ -26,7 +26,10 @@ OBJS	= main.o \
 
 BUILD_OBJS = $(foreach obj,$(OBJS),$(BUILD)/$(obj))
 
-all: $(BIN)/$(BINARY)
+all: $(BIN)/$(BINARY) $(BIN)/xlib-shim.so
+
+$(BIN)/xlib-shim.so:
+	gcc -fPIC $(CFLAGS) -shared -o $@ xlib-shim.c
 
 $(BUILD)/%.o: %.c
 	@mkdir -p $(dir $@)

client/xlib-shim.c

@@ -0,0 +1,15 @@
+#include <X11/Xlib.h>
+#include <stdbool.h>
+#include "debug.h"
+
+int XSync(Display * display, Bool discard)
+{
+  static bool doneInfo = false;
+  if (!doneInfo)
+  {
+    DEBUG_INFO("XSync Override Enabled");
+    doneInfo = true;
+  }
+
+  return 0;
+}