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: I884a78b67679c1f0b90a6c0159b17ab007f8cc60
diff --git a/libc/system_properties/contexts_split.cpp b/libc/system_properties/contexts_split.cpp
index 3579f55..78bdc64 100644
--- a/libc/system_properties/contexts_split.cpp
+++ b/libc/system_properties/contexts_split.cpp
@@ -281,7 +281,7 @@
   return true;
 }
 
-bool ContextsSplit::Initialize(bool writable, const char* filename, bool* fsetxattr_failed) {
+bool ContextsSplit::Initialize(bool writable, const char* filename, bool* fsetxattr_failed, bool) {
   filename_ = filename;
   if (!InitializeProperties()) {
     return false;