disable unused parameter warning

cpuid, scale_neon, planarfunctions and jpeg have internal API's
with specialized versions that do not use all parameters.
Disable the warning in Android.mk for now.

BUG=libyuv:681
TEST=android make builds without warning.

Change-Id: I72ee654c376c6dd85b616fc4438e3ad0a86b39bc
Reviewed-on: https://chromium-review.googlesource.com/440510
Commit-Queue: Frank Barchard <fbarchard@google.com>
Reviewed-by: Henrik Kjellander <kjellander@chromium.org>

Android.mk

@@ -44,6 +44,8 @@ LOCAL_SRC_FILES := \
 #   source/convert_jpeg.cc
 #   source/mjpeg_validate.cc
 
+LOCAL_CFLAGS += -Wno-unused-parameter
+
 ifeq ($(TARGET_ARCH_ABI),armeabi-v7a)
     LOCAL_CFLAGS += -DLIBYUV_NEON
     LOCAL_SRC_FILES += \