Keep the dynamic linker's soinfo pools mostly read-only.

We'll need a lot more refactoring of this code before we can reduce
the granularity, but this is a step forward.

Change-Id: I07061720e734b571a8399c1d5b4f2f35cd681307

linker/debugger.cpp

@@ -32,7 +32,6 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <unistd.h>
-#include <stdbool.h>
 #include <signal.h>
 #include <sys/prctl.h>
 #include <errno.h>