Also pass SYSTEMSERVERCLASSPATH to compsvc

Like the existing two, this is a temporary workaround to unblock
development, until we can run derive_classpath in the VM.

Bug: 205750213
Test: can use the variable locally
Change-Id: Ib38a0a1d22fc4528832a1abbb6a26fb9148034c7
diff --git a/compos/src/compsvc.rs b/compos/src/compsvc.rs
index 2a5534c..9d2f1dc 100644
--- a/compos/src/compsvc.rs
+++ b/compos/src/compsvc.rs
@@ -90,10 +90,12 @@
         &self,
         boot_classpath: &str,
         dex2oat_boot_classpath: &str,
+        system_server_classpath: &str,
     ) -> BinderResult<()> {
         // TODO(198211396): Implement correctly.
         env::set_var("BOOTCLASSPATH", boot_classpath);
         env::set_var("DEX2OATBOOTCLASSPATH", dex2oat_boot_classpath);
+        env::set_var("SYSTEMSERVERCLASSPATH", system_server_classpath);
         Ok(())
     }