Use -Werror in external/fsck_msdos

* Fix old redefined error of LOCAL_CFLAGS.

Bug: 66996870
Test: build with WITH_TIDY=1
Change-Id: I8f06425595cf1fbce8d1e124536a5cf1dfdc360b
diff --git a/Android.mk b/Android.mk
index 534a478..8dec83a 100644
--- a/Android.mk
+++ b/Android.mk
@@ -6,9 +6,15 @@
 
 LOCAL_C_INCLUDES := external/fsck_msdos/
 
-LOCAL_CFLAGS := -O2 -g -W -Wall -D_BSD_SOURCE -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64
-
-LOCAL_CFLAGS := -Wno-unused-variable -Wno-unused-const-variable -Wno-format -Wno-sign-compare
+LOCAL_CFLAGS := -O2 -g \
+    -Wall -Werror \
+    -D_BSD_SOURCE \
+    -D_LARGEFILE_SOURCE \
+    -D_FILE_OFFSET_BITS=64 \
+    -Wno-unused-variable \
+    -Wno-unused-const-variable \
+    -Wno-format \
+    -Wno-sign-compare
 
 LOCAL_MODULE := fsck_msdos
 LOCAL_MODULE_TAGS :=