If we're not touching them, we don't need to do anything special to pass
them along -- with one important caveat: due to how cmake arguments
work, the implicitly passed arguments need to be specified before
arguments that we handle.

This isn't particularly nice, but the alternative is enumerating all
arguments that can be used by llvm_add_library and the macros it calls
(it also relies on implicit passing of some arguments to
llvm_process_sources).

By adding signal codes to UnixSignals and adding a new function
where you can get a string with optional address and bounds.

Added signal codes to the Linux, FreeBSD and NetBSD signal sets.
I've checked the numbers against the relevant sources.

Each signal code has a code number, description and printing options.
By default you just get the descripton, you can opt into adding either
a fault address or bounds information.

Bounds signals we'll use the description, unless we have the bounds
values in which case we say whether it is an upper or lower bound
issue.

GetCrashReasonString remains in CrashReason because we need it to
be compiled only for platforms with siginfo_t. Ideally it would
move into NativeProcessProtocol, but that is also used
by NativeRegisterContextWindows, where there would be no siginfo_t.

Reviewed By: JDevlieghere

Differential Revision: https://reviews.llvm.org/D146044

This reverts commit 71c4d186f1cf247f1aa45f4fd1b38f350b68d123.
The reinterpret casts were not needed.

This reverts commit af38530ee29c285f3827e33a41edf27c9c3a6767 due
to a build failure on 32 bit.

So that there is only one function that NativeThreads call,
which takes a siginfo. Everything else is an internal detail.

Reviewed By: labath, JDevlieghere

Differential Revision: https://reviews.llvm.org/D146043

As preferred by the llvm guidelines.

The last user was ProcessMessage, which has itself been removed.

Reviewed By: emaste

Differential Revision: https://reviews.llvm.org/D145561

The last use of these was removed in cd443398566b953642ead7c81528ab5b4e211eb9.

Reviewed By: emaste

Differential Revision: https://reviews.llvm.org/D145559

This patch replaces (llvm::|)Optional< with std::optional<.  I'll post
a separate patch to clean up the "using" declarations, #include
"llvm/ADT/Optional.h", etc.

This is part of an effort to migrate from llvm::Optional to
std::optional:

https://discourse.llvm.org/t/deprecating-llvm-optional-x-hasvalue-getvalue-getvalueor/63716