Explicitly load shared libraries with local visibility.

On some platforms the default is undefined if neither RTLD_GLOBAL
nor RTLD_LOCAL is specified.

Bug 25282950

Change-Id: I0aea6a9f604afa0412a8f6d9c614b18987fbf514
Reviewed-on: https://swiftshader-review.googlesource.com/4190
Reviewed-by: Nicolas Capens <capn@google.com>
Tested-by: Nicolas Capens <capn@google.com>