Re-land r313210 - Fix for bug 34532 - A few rough corners related to...

Re-land r313210 - Fix for bug 34532 - A few rough corners related to post-mortem debugging (core/minidump)

The main change is to avoid setting the process state as running when
debugging core/minidumps (details in the bug).  Also included a few small,
related fixes around how the errors propagate in this case.

Fixed the FreeBSD/Windows break: the intention was to keep
Process::WillResume() and Process::DoResume() "in-sync", but this had the
unfortunate consequence of breaking Process sub-classes which don't override
WillResume().

The safer approach is to keep Process::WillResume() untouched and only
override it in the minidump and core implementations.

patch by lemo

Bug: https://bugs.llvm.org/show_bug.cgi?id=34532

Differential Revision: https://reviews.llvm.org/D37651

llvm-svn: 313655