exceptions: evaluate needed exceptions in upstream

This is largely a more speculative issue. According to analysis of sections within compilation units, most source files end up having a not insignificant size proportion in exception tables. @Reflejo recommended analyzing cases where exceptions might lead to irrecoverable conditions.

### Size Win

per https://github.com/lyft/envoy-mobile/issues/17#issuecomment-504290445

> On the stripped binary there is also at least 1MB of exception tables. I don't know how many of them are exceptions we recover from vs we terminate. So we might investigate adding the nothrow specifier on methods so the except table is not created (not sure how we'll do this in an elegant way only for mobile, nor how we use exceptions, just throwing this here as a thought)