Do not assert on POSIXDYLD double-eAdd.

Summary:
This has been discovered while experimenting with the gecko linker on android.
In general, assert()'ing on "user input" is a bad idea.

Test Plan: Run unit tests.

Reviewers: clayborg, tfiala

Subscribers: lldb-commits

Differential Revision: http://reviews.llvm.org/D8495

llvm-svn: 232966