Make build of loopfiltermask.c conditional

Change-Id: I2bda80b0f026c0e269ec2953a26945d2a6e53d98
diff --git a/av1/av1.cmake b/av1/av1.cmake
index b817fd0..06b448b 100644
--- a/av1/av1.cmake
+++ b/av1/av1.cmake
@@ -50,7 +50,6 @@
             "${AOM_ROOT}/av1/common/frame_buffers.h"
             "${AOM_ROOT}/av1/common/idct.c"
             "${AOM_ROOT}/av1/common/idct.h"
-            "${AOM_ROOT}/av1/common/loopfiltermask.c"
             "${AOM_ROOT}/av1/common/mv.h"
             "${AOM_ROOT}/av1/common/mvref_common.c"
             "${AOM_ROOT}/av1/common/mvref_common.h"
@@ -89,6 +88,10 @@
             "${AOM_ROOT}/av1/common/warped_motion.c"
             "${AOM_ROOT}/av1/common/warped_motion.h")
 
+if(CONFIG_LPF_MASK)
+  list(APPEND AOM_AV1_COMMON_SOURCES "${AOM_ROOT}/av1/common/loopfiltermask.c")
+endif()
+
 list(APPEND AOM_AV1_DECODER_SOURCES
             "${AOM_ROOT}/av1/av1_dx_iface.c"
             "${AOM_ROOT}/av1/decoder/decodeframe.c"