Fix backwards compatible system property structure

The original structure included four reserved 32-bit values. This
change adds these back into the structure so that the
__system_property_find_compat function will (again) process the system
properties correctly.
diff --git a/libc/bionic/system_properties_compat.c b/libc/bionic/system_properties_compat.c
index 6dbc4cc..0326f05 100644
--- a/libc/bionic/system_properties_compat.c
+++ b/libc/bionic/system_properties_compat.c
@@ -48,6 +48,7 @@
     unsigned volatile serial;
     unsigned magic;
     unsigned version;
+    unsigned reserved[4];
     unsigned toc[1];
 };