Change MemMap::maps_ to not be global variable

Runtime.exit() was causing globals to get destructed at the same time
that another thread was using it for allocating a new mem map.

(cherry picked from commit 6e88ef6b604a7a945a466784580c42e6554c1289)

Bug: 17962201
Change-Id: I400cb7b8141d858f3c08a6fe59a02838c04c6962
diff --git a/patchoat/patchoat.cc b/patchoat/patchoat.cc
index a9b2a43..74f6779 100644
--- a/patchoat/patchoat.cc
+++ b/patchoat/patchoat.cc
@@ -761,6 +761,7 @@
 
 static int patchoat(int argc, char **argv) {
   InitLogging(argv);
+  MemMap::Init();
   const bool debug = kIsDebugBuild;
   orig_argc = argc;
   orig_argv = argv;