Enable `asan/TestCases/Posix/start-deactivated.cc` test for iOS.

Summary:
To make this test pass it was necesary to change `iossim_run.py` to
propagate the `ASAN_ACTIVATION_OPTIONS` environment variable into the
testing environment.

rdar://problem/49114807

Reviewers: kubamracek, yln, serge-sans-paille

Subscribers: #sanitizers, llvm-commits

Tags: #sanitizers, #llvm

Differential Revision: https://reviews.llvm.org/D59660

llvm-svn: 356701