Add lldb-gdbserver support for Linux x86_64.

This change brings in lldb-gdbserver (llgs) specifically for Linux x86_64.
(More architectures coming soon).

Not every debugserver option is covered yet.  Currently
the lldb-gdbserver command line can start unattached,
start attached to a pid (process-name attach not supported yet),
or accept lldb attaching and launching a process or connecting
by process id.

The history of this large change can be found here:
https://github.com/tfiala/lldb/tree/dev-tfiala-native-protocol-linux-x86_64

Until mid/late April, I was not sharing the work and continued
to rebase it off of head (developed via id tfiala@google.com).  I switched over to
user todd.fiala@gmail.com in the middle, and once I went to github, I did
merges rather than rebasing so I could share with others.


git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@212069 91177308-0d34-0410-b5e6-96231b3b80d8
Fixup Windows build breaks for the llgs upstream.

Also moves NativeRegisterContextLinux* files into the Linux directory.
These, like NativeProcessLinux, should only be built on Linux or a cross
compiler with proper headers.


git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@212074 91177308-0d34-0410-b5e6-96231b3b80d8
Fix Windows build after llgs upstream.

With _HAS_EXCEPTIONS=0, Windows' version of <thread> will fail to
compile because it calls __uncaught_exception(), which is compiled
out due to _HAS_EXCEPTIONS=0.  This just creates a stub version
of __uncaught_exception() which always fails.

git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@212076 91177308-0d34-0410-b5e6-96231b3b80d8
Merge upstream llvm.org r212107.

This change fixes up the https://github.com/tfiala/lldb master
branch to be identical to llvm.org r212107.

We are not checking any changes directly into the master branch.
This should be a read-only copy of upstream llvm.org.