Fixed the "mmap" to work on MacOSX/darwin by supplying the correct arguemnts.

Modified ClangUserExpression and ClangUtilityFunction to display the actual
error (if one is available) that made the JIT fail instead of a canned 
response.

Fixed the restoring of all register values when the 'G' packet doesn't work
to use the correct data.

llvm-svn: 131454