Accommodate [[nodiscard]] std::lock_guard in updated libc++

A newer version of libc++ makes the std::lock_guard constructor
[[nodiscard]] as an extension to the C++ standard, and a NOLINT comment
is insufficient. Fix these errors:

system/incremental_delivery/libdataloader/DataLoaderConnector.cpp:404:9: error: ignoring temporary created by a constructor declared with 'nodiscard' attribute [-Werror,-Wunused-value]
        std::lock_guard{mPendingReadsLooperBusy}; //NOLINT
        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
system/incremental_delivery/libdataloader/DataLoaderConnector.cpp:405:9: error: ignoring temporary created by a constructor declared with 'nodiscard' attribute [-Werror,-Wunused-value]
        std::lock_guard{mLogLooperBusy}; //NOLINT
        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Bug: b/175635923
Test: treehugger
Change-Id: I6d43c136e80e203e726dd896913241b195e76af5
1 file changed