SERVER-27244 Status usage compile-time facilities.

There are numerous places in the codebase where `mongo::Status` or
`mongo::StatusWith< T >` objects are returned and never checked.
Many of these are innocuous, but many of them are potentially
severe bugs.  This change introduces facilities to permit
compile-time warning of unchecked `Status` and `StatusWith` usage
on clang compilers.  It introduces an `ignore` function which is
useful to state that a specific "ignored status" case was
intentional.  It not presently an error, in clang builds, to
forget to check a `Status` -- this will come in a later commit.

This also introduces a `transitional_ignore` function, which allows
for easy continual auditing of the codebase for current "whitelisted"
unchecked-status instances.  All present "ignored status" cases
have been marked `transitional_ignore`.

1 files changed, 5 insertions, 3 deletions

diff --git a/src/mongo/s/query/async_results_merger.cpp b/src/mongo/s/query/async_results_merger.cpp
index ced16197e98..037765fd5f9 100644
--- a/src/mongo/s/query/async_results_merger.cpp
+++ b/src/mongo/s/query/async_results_merger.cpp
@@ -525,9 +525,11 @@ void AsyncResultsMerger::scheduleKillCursors_inlock(OperationContext* opCtx) {
             executor::RemoteCommandRequest request(
                 remote.getTargetHost(), _params->nsString.db().toString(), cmdObj, opCtx);
 
-            _executor->scheduleRemoteCommand(
-                request,
-                stdx::bind(&AsyncResultsMerger::handleKillCursorsResponse, stdx::placeholders::_1));
+            _executor
+                ->scheduleRemoteCommand(request,
+                                        stdx::bind(&AsyncResultsMerger::handleKillCursorsResponse,
+                                                   stdx::placeholders::_1))
+                .status_with_transitional_ignore();
         }
     }
 }