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/ScopedDisableMalloc.h b/libmemunreachable/ScopedDisableMalloc.h
index 7d2f630..655e826 100644
--- a/libmemunreachable/ScopedDisableMalloc.h
+++ b/libmemunreachable/ScopedDisableMalloc.h
@@ -25,6 +25,8 @@
 #include "bionic.h"
 #include "log.h"
 
+namespace android {
+
 class DisableMallocGuard {
  public:
   DisableMallocGuard() : disabled_(false) {}
@@ -102,4 +104,6 @@
   DisableMallocGuard disable_malloc_;
 };
 
+}  // namespace android
+
 #endif  // LIBMEMUNREACHABLE_SCOPED_DISABLE_MALLOC_H_