[lldb] [lldb-server] Catch and report errors from main loop
[lldb] [lldb-server] Catch and report errors from main loop

Catch the possible error from lldb-gdbserver's main loop, and report
it verbosely.  Currently, if the loop fails the server exits normally,
rendering the problem indistinguishable from regular termination.

Differential Revision: https://reviews.llvm.org/D58228

git-svn-id: 4c4cc70b1ef44ba2b7963015e681894188cea27e@354030 91177308-0d34-0410-b5e6-96231b3b80d8

apple/swift-lldb,llvm-mirror/lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,llvm-mirror/lldb,llvm-mirror/lldb,llvm-mirror/lldb,llvm-mirror/lldb,apple/swift-lldb,apple/swift-lldb