Fix makefile for x11 dependency flags

BUG=chromium:381565
TEST=build with USE_VAAPI=yes
Change-Id: Ia6fb94593f6adfb35b084311aa9122a9723a9cbc
Reviewed-on: https://chromium-review.googlesource.com/203230
Reviewed-by: Pawel Osciak <posciak@chromium.org>
Tested-by: Kuang-che Wu <kcwu@chromium.org>
Commit-Queue: Kuang-che Wu <kcwu@chromium.org>
diff --git a/Makefile b/Makefile
index 7d85181..7224708 100644
--- a/Makefile
+++ b/Makefile
@@ -9,7 +9,7 @@
 USE_VAAPI ?= $(if $(filter $(ARCH),amd64 x86),yes,no)
 ifeq ($(USE_VAAPI),yes)
   CPPFLAGS += -DHAS_VAAPI
-  PC_DEPS += libva-x11
+  PC_DEPS += libva-x11 x11
   VAAPI_OBJS = util_vaapi.o
 endif