Refactoring for struct UserArea:

- Decouples RegisterContext_x86_64 from UserArea.
- Restores the original definition of UserArea so that it can be used to generate offsets for use with ptrace.
- Moves UserArea to the 64-bit Linux specialization.

- Also fixes an off-by-one error for the size of m_gpr.
- Also adds a TODO comment noting the need for a mechanism to identify the correct plugin based on the target OS (and architecture).

Reviewed by: Matt Kopec and Samuel Jacob

llvm-svn: 181055

lldb/source/Plugins/Process/POSIX/POSIXThread.cpp

@@ -99,6 +99,8 @@ POSIXThread::GetRegisterContext()
             break;
 
         case ArchSpec::eCore_x86_64_x86_64:
+// TODO: Use target OS/architecture detection rather than ifdefs so that
+// lldb built on FreeBSD can debug on Linux and vice-versa.
 #ifdef __linux__
             m_reg_context_sp.reset(new RegisterContextLinux_x86_64(*this, 0));
 #endif