Check calling user in composd.

Access to our service is already restricted by selinux, so this is
really just an extra safety check.

Test: Run composd
Bug: 186126194
Change-Id: Ib997c4bb282ac1c3d654d57bb84845a455893f2c
diff --git a/compos/composd/Android.bp b/compos/composd/Android.bp
index ecfea61..8391ed6 100644
--- a/compos/composd/Android.bp
+++ b/compos/composd/Android.bp
@@ -19,6 +19,7 @@
         "libcomposd_native_rust",
         "libnum_traits",
         "liblog_rust",
+        "librustutils",
         "libshared_child",
     ],
     proc_macros: ["libnum_derive"],