Move x86-specific struct user code for Linux ProcessMonitor behind #define guards.

See http://reviews.llvm.org/D4092 for details.

Change by Paul Osmialowski.  (Minor tweaks to the comment by Todd.)


git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@211026 91177308-0d34-0410-b5e6-96231b3b80d8