Always use our copy of libz

Instead of hoping that the host libz is compatible with our build time
stubs.

Also removes -lpthread, which is now automatically added for host tools.

Test: m mksquashfs
Change-Id: I564f77ec4b5c3622e39f0505d507283aab142335
diff --git a/squashfs-tools/Android.mk b/squashfs-tools/Android.mk
index 74d042f..10b45b6 100644
--- a/squashfs-tools/Android.mk
+++ b/squashfs-tools/Android.mk
@@ -35,9 +35,9 @@
                 -Wno-unused-parameter -Wno-sign-compare -Wno-pointer-arith -Wno-missing-field-initializers \
                 -Wno-unused-function -Werror
 
-LOCAL_LDLIBS := -lpthread -lm -lz
+LOCAL_LDLIBS := -lm
 
 LOCAL_SHARED_LIBRARIES := libcutils libselinux
-LOCAL_STATIC_LIBRARIES := liblz4
+LOCAL_STATIC_LIBRARIES := liblz4 libz
 
 include $(BUILD_HOST_EXECUTABLE)