[DWP] add overflow check for llvm-dwp tools if offset overflow

Now, if the offset overflow happens, we just silently ignore it.
We will generate a bad dwp file, which will crash the gdb or make
it undefined behavior, and hard to address the root cause. So, we
need to produce some messages if overflow happens.

Reviewed By: ayermolo, dblaikie, steven.zhang

Differential Revision: https://reviews.llvm.org/D144565