[BOLT] Fix relocation verification

Summary:
We verify that relocation information matches a value stored in a
binary, i.e. "ExtractedValue == SymbolValue + Addend". However, because
of the size of the relocation, and the fact that an addend is always
of type int64_t, we have to sign-extend the extracted value, and then we
might get mismatch in higher bits in certain scenarios. Hence, we should
only compare values that are truncated to a relocation size.

Discovered while processing hhvm binary with modified compiler flags.

(cherry picked from FBD7462559)