Invalidate symbolizer module list from dlopen/dlclose interceptors

Summary:
The module list should only be invalidated by dlopen and dlclose,
so the symbolizer should only re-generate it when we've hit one of those functions.

Reviewers: kubamracek, rnk, vitalybuka

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D37268

llvm-svn: 314219