Fix build error on slaves about ucontext_t usage in the handler_3_t typedef
Fix build error on slaves about ucontext_t usage in the handler_3_t typedef

Moves ucontext.h and unistd.h header inclusion earlier and makes it unconditional on Linux.  The unistd.h include is needed for getpid() usage in infloop.c.

Review URL: https://codereview.appspot.com/6654047

git-svn-id: ed337ca7cdb08c0ba29d8fe58632bb7686892c2d@1658 49cc7528-f6fd-11dd-9d1a-b59b2e1864b6

rnk/dynamorio,rnk/dynamorio,rnk/dynamorio,rnk/dynamorio,rnk/dynamorio