Build fails as TaggedPtr is undefined for Power PC

Couchbase build fails with error "#error "TaggedPtr is x64 specific code. Not tested on other architectures"

To add check for powerpc64 architecture, following change needs to be added:

diff --git a/engines/ep/src/tagged_ptr.h b/engines/ep/src/tagged_ptr.h
index 9ecd6ae..959c8cd 100644
— a/engines/ep/src/tagged_ptr.h
+++ b/engines/ep/src/tagged_ptr.h
@@ -19,7 +19,7 @@

#include <memory>

-#if !_x86_64_ && !_M_X64
+#if !_x86_64_ && !_M_X64 && !_powerpc64_
#error "TaggedPtr is x64 specific code. Not tested on other architectures"
#endif