Don't specify -std=gnu99 for C++ builds -- it breaks clang

Signed-off-by: Bernhard Rosenkränzer <Bernhard.Rosenkranzer@linaro.org>
diff --git a/Android.mk b/Android.mk
index 1e0d71e..3b8da66 100644
--- a/Android.mk
+++ b/Android.mk
@@ -36,7 +36,7 @@
     -DWAFFLE_ANDROID_MINOR_VERSION=$(waffle_android_minor_version) \
     -Wno-pointer-arith
 
-LOCAL_CFLAGS += -std=c99
+LOCAL_CONLYFLAGS += -std=c99
 
 LOCAL_C_INCLUDES := \
     $(LOCAL_PATH)/include/waffle \