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/PtracerThread.cpp b/libmemunreachable/PtracerThread.cpp
index 41efa9c..aca2a82 100644
--- a/libmemunreachable/PtracerThread.cpp
+++ b/libmemunreachable/PtracerThread.cpp
@@ -35,6 +35,8 @@
 #include "anon_vma_naming.h"
 #include "log.h"
 
+namespace android {
+
 class Stack {
  public:
   explicit Stack(size_t size) : size_(size) {
@@ -148,3 +150,5 @@
 void PtracerThread::ClearTracer() {
   prctl(PR_SET_PTRACER, 0);
 }
+
+}  // namespace android