Added gdb-remote tests for Q{Save,Restore}RegisterState.

Tests for both thread suffix and no thread suffix execution.

Moved some bit-flipping helper methods from TestLldbGdbServer
into the base GdbRemoteTestCaseBase class.


git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@211381 91177308-0d34-0410-b5e6-96231b3b80d8