Sometimes we need to know the size of a symbol besides its address, so
maybe we can start using the existing `BOLTLinker::lookupSymbolInfo()`
(that returns symbol address and size) and remove
`BOLTLinker::lookupSymbol()` (that only returns symbol address). And for
both we need to check return value as it is wrapped in `std::optional<>`,
which makes the difference even smaller.
9fa77c1854