gdb-remote signal delivery test cleanup.

Learned that MacOSX only accepts signal delivery on a thread that is
already signal handling.  Reworked the test exe to cause a SIGSEGV
and recover if either nothing intercepts the SIGSEGV handler, or
if a SIGUSR1 is inserted.  The test uses the latter part to test
signal delivery on continue using the SIGUSR1.

I still don't have this working on MacOSX.  I'm seeing the
signal get delivered to a different thread than the one I'm
specifying with $Hc{thread-id} + $C{signo}, or with
$vCont;C{signo}:{thread-id};c.  I'll come back to this
after getting it working on the llgs branch on Linux x86_64.



git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@209912 91177308-0d34-0410-b5e6-96231b3b80d8
Merge upstream r209912 into dev-tfiala-native-protocol-linux-x86_64
Implemented $C{signal-number} for llgs/linux.

Enabled $Hc then $C{signal-number} test for llgs.

Modified NativeThreadLinux signal handlers to be instance methods
instead of static class methods.  Reduces unneeded error correction
and instance pointer usage.

Added gdb-remote packets logging of IllFormed packets in SendIllFormedResponse().

Added NativeThreadProtocol::TranslateStopInfoToGdbSignal(...) and it
is overridden for NativeThreadLinux to translate Linux signals that
map to Gdb special signals in cases where those are needed (e.g. SIGSEGV).
The default NativeThreadProtocol does not translate anything.
Follow-up task for figuring out how exception stop info details get
handled exactly.  An earlier form of this function existed but it
wasn't implemented.

Fixed up Linux SIGSEGV handling which assumed the process crashed at
the pre-announce phase when, in reality, that is just an announcement
that a SIGSEGV is about to arrive, which might get handled by a signal
handler within the inferior, which might not crash.  (This is indeed
the non-crash case that the test exe makes use of to trigger a signal
on a specific thread).  Follow-up tasks are to correct SIGILL and
similar signals that are equally marking a crash prematurely on initial
signal delivery notification.