Cache memory regions in ProcessMinidump and use the linux maps as the source of the information if available

Breakpad creates minidump files that sometimes have:
- linux maps textual content
- no MemoryInfoList

Right now unless the file has a MemoryInfoList we get no region information.

This patch:

- reads and caches the memory region info one time and sorts it for easy subsequent access
- get the region info from the best source in this order:
  - linux maps info (if available)
  - MemoryInfoList (if available)
  - MemoryList or Memory64List
- returns memory region info for the gaps between regions (before the first and after the last)

Differential Revision: https://reviews.llvm.org/D55522
13 files changed