POSIX dyld: handle extra MIPS link map field

On at least FreeBSD and NetBSD there is an extra field in the dyld link
map struct.  I've left an assert for other OSes (i.e., Linux/mips) until
it's determined if they do the same.


git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@192358 91177308-0d34-0410-b5e6-96231b3b80d8