zstd: Android.bp: Allow rsync to add zstd compression support

Change-Id: Ic92ad997f9b8dd4686df1e1fa5d0dfb88fdab345

Author: DroidFreak32

Android.bp

@@ -103,6 +103,7 @@ cc_library {
         "//external/dwarves:__subpackages__",
         "//external/elfutils:__subpackages__",
         "//external/libbpf:__subpackages__",
+        "//external/rsync:__subpackages__",
         "//external/squashfs-tools/squashfs-tools:__subpackages__",
         "//external/stg:__subpackages__",
         "//frameworks/libs/binary_translation/tools:__subpackages__",
@@ -118,6 +119,7 @@ cc_library {
     product_available: true,
     recovery_available: true,
     vendor_available: true,
+    system_ext_specific: true,
     host_supported: true,
     native_bridge_supported: true,
     ramdisk_available: true,