Log the error message when failing to mount/umount.

Test: Observe the error messaage for a umount failure case.
Bug: 36686818
Change-Id: I28e335c2df4454dd0192f95e3909599fcc9dc1c0
diff --git a/Android.mk b/Android.mk
index 58b8a22..037aa16 100644
--- a/Android.mk
+++ b/Android.mk
@@ -29,9 +29,11 @@
 # ===============================
 include $(CLEAR_VARS)
 LOCAL_SRC_FILES := mounts.cpp
-LOCAL_CLANG := true
-LOCAL_CFLAGS := -Wall -Wno-unused-parameter -Werror
+LOCAL_CFLAGS := \
+    -Wall \
+    -Werror
 LOCAL_MODULE := libmounts
+LOCAL_STATIC_LIBRARIES := libbase
 include $(BUILD_STATIC_LIBRARY)
 
 # recovery (static executable)