Mark libselinux as VNDK in Android.bp

This commit marks libselinux.so as VNDK, so that vendor variant of
libselinux.so can be installed into /system/lib[64]/vndk instead of
/vendor/lib[64].  This makes it easier to apply security patches
through system-only OTAs.

Before this commit, libselinux was not an VNDK library because there
was a concern with selabel database file format.  This is no longer a
concern because the file backend is disabled in vendor variant.

Bug: 69587962
Bug: 63866913
Test: /system/lib64/vndk/libselinux.so shows up in GSI
Change-Id: I9d3be760bb5b3f8bf50b96ce6d8b938bf75c620a

CleanSpec.mk

@@ -3,3 +3,4 @@
 #
 $(call add-clean-step, rm -rf $(OUT_DIR)/host/linux-x86/bin/audit2allow)
 $(call add-clean-step, rm -rf $(OUT_DIR)/host/linux-x86/bin/audit2why)
+$(call add-clean-step, rm -rf $(PRODUCT_OUT)/vendor/lib/libselinux.so)

libselinux/Android.bp

@@ -105,7 +105,12 @@ cc_defaults {
 cc_library {
     name: "libselinux",
     defaults: ["libselinux_defaults"],
+
     vendor_available: true,
+    vndk: {
+        enabled: true,
+    },
+
     host_supported: true,
     cflags: ["-DUSE_PCRE2"],