Write appcompat_override system properties

Create a second set of system properties, that can be overlaid over the
real ones if necessary, for appcompat purposes.

Bug: 291814949
Ignore-AOSP-First: Aosp -> internal merge conflict
Test: manual, treehugger, system_properties_test

Change-Id: I541d3658cab7753c16970957c6ab4fc8bd68d8f3
Merged-In: I884a78b67679c1f0b90a6c0159b17ab007f8cc60
diff --git a/libc/libc.map.txt b/libc/libc.map.txt
index 824682b..d737946 100644
--- a/libc/libc.map.txt
+++ b/libc/libc.map.txt
@@ -1806,6 +1806,7 @@
     __system_property_area_init;
     __system_property_set_filename;
     __system_property_update;
+    __system_properties_reload;
     android_fdsan_get_fd_table;
     android_fdtrack_compare_exchange_hook; # llndk
     android_fdtrack_get_enabled; # llndk