[HWASan] Add sizeof(global) in report even if symbols missing.

Summary: Refactor the current global header iteration to be callback-based, and add a feature that reports the size of the global variable during reporting. This allows binaries without symbols to still report the size of the global variable, which is always available in the HWASan globals PT_NOTE metadata.

Reviewers: eugenis, pcc

Reviewed By: pcc

Subscribers: mgorny, llvm-commits, #sanitizers

Tags: #sanitizers, #llvm

Differential Revision: https://reviews.llvm.org/D80599