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, 1 insertions, 1 deletions

diff --git a/src/mongo/db/service_liason_mock.cpp b/src/mongo/db/service_liason_mock.cpp
index b7b03ba9ceb..4c2ba699acb 100644
--- a/src/mongo/db/service_liason_mock.cpp
+++ b/src/mongo/db/service_liason_mock.cpp
@@ -39,7 +39,7 @@ MockServiceLiasonImpl::MockServiceLiasonImpl() {
     auto timerFactory = stdx::make_unique<executor::AsyncTimerFactoryMock>();
     _timerFactory = timerFactory.get();
     _runner = stdx::make_unique<PeriodicRunnerASIO>(std::move(timerFactory));
-    _runner->startup();
+    _runner->startup().transitional_ignore();
 }
 
 LogicalSessionIdSet MockServiceLiasonImpl::getActiveSessions() const {