Check if removal of MethodByName() call can improve dead code elimination.

[jmalloc]

See golang/protobuf#1561

We use it here:

testkit/location/location.go

Line 115 in f03ed61

rm, ok := rt.MethodByName(m)

It may not matter much since this code would generally only be used from test packages, but it'd be good to confirm that they are still eliminated properly. It's also not that uncommon to have some tests in the non-test package to test unexported functions, though this should be rare with Dogma applications.