Move libmemunreachable into namespace android

Putting libmemunreachable in the global C++ namespace was an oversight,
move it into namespace android.

Test: m -j checkbuild
Change-Id: I0799906f6463178cb04a719bb4054cad33a50dbe
diff --git a/libmemunreachable/ScopedSignalHandler.h b/libmemunreachable/ScopedSignalHandler.h
index 58ac2aa..f62f368 100644
--- a/libmemunreachable/ScopedSignalHandler.h
+++ b/libmemunreachable/ScopedSignalHandler.h
@@ -26,6 +26,8 @@
 
 #include "log.h"
 
+namespace android {
+
 class ScopedSignalHandler {
  public:
   using Fn = std::function<void(ScopedSignalHandler&, int, siginfo_t*, void*)>;
@@ -74,4 +76,6 @@
   static SignalFn handler_;
 };
 
+}  // namespace android
+
 #endif  // LIBMEMUNREACHABLE_SCOPED_SIGNAL_HANDLER_H_