[lldb] Enable "frame diagnose" on linux (#123217)

.. by changing the signal stop reason format :facepalm:

The reason this did not work is because the code in
`StopInfo::GetCrashingDereference` was looking for the string "address="
to extract the address of the crash. Macos stop reason strings have the
form
```
  EXC_BAD_ACCESS (code=1, address=0xdead)
```
while on linux they look like:
```
  signal SIGSEGV: address not mapped to object (fault address: 0xdead)
```

Extracting the address from a string sounds like a bad idea, but I
suppose there's some value in using a consistent format across
platforms, so this patch changes the signal format to use the equals
sign as well. All of the diagnose tests pass except one, which appears
to fail due to something similar #115453 (disassembler reports
unrelocated call targets).

I've left the tests disabled on windows, as the stop reason reporting
code works very differently there, and I suspect it won't work out of
the box. If I'm wrong -- the XFAIL will let us know.