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/ThreadCapture.h b/libmemunreachable/ThreadCapture.h
index d209660..961cb60 100644
--- a/libmemunreachable/ThreadCapture.h
+++ b/libmemunreachable/ThreadCapture.h
@@ -21,6 +21,8 @@
 
 #include "Allocator.h"
 
+namespace android {
+
 struct ThreadInfo {
   pid_t tid;
   allocator::vector<uintptr_t> regs;
@@ -51,4 +53,6 @@
   Allocator<ThreadCaptureImpl>::unique_ptr impl_;
 };
 
+}  // namespace android
+
 #endif