Checks for types which can be made trivially-destructible by removing
out-of-line defaulted destructor declarations.
The check is motivated by the work on C++ garbage collector in Blink
(rendering engine for Chrome), which strives to minimize destructors and
improve runtime of sweeping phase.
In the entire chromium codebase the check hits over 2000 times.
Differential Revision: https://reviews.llvm.org/D69435