Fix fail over to vfat from exfat

Fix issues with MD5 checking using chdir and leaving the working
dir in a subfolder that prevented unmounting sometimes.

Change-Id: I01a563d722f474297ed3f7a30064c3a61748ade3
diff --git a/Android.mk b/Android.mk
index 3cfd1fb..de25ff2 100644
--- a/Android.mk
+++ b/Android.mk
@@ -188,6 +188,9 @@
 ifeq ($(TW_FORCE_CPUINFO_FOR_DEVICE_ID), true)
     LOCAL_CFLAGS += -DTW_FORCE_CPUINFO_FOR_DEVICE_ID
 endif
+ifeq ($(TW_NO_EXFAT_FUSE), true)
+    LOCAL_CFLAGS += -DTW_NO_EXFAT_FUSE
+endif
 ifeq ($(TW_INCLUDE_CRYPTO), true)
     LOCAL_CFLAGS += -DTW_INCLUDE_CRYPTO
     LOCAL_CFLAGS += -DCRYPTO_FS_TYPE=\"$(TW_CRYPTO_FS_TYPE)\"