folly: allow demangling very large symbols
folly: allow demangling very large symbols

Summary:
Newer libiberty has limits that over constrain
the size of symbols that can be demangled.
This applies the same adjustment in the default
platform009 demangler, done in D26380825

Differential Revision: D26617797

fbshipit-source-id: 8d3e72a0807aa9ecff18d26f38c1acb83f9c051b

facebook/folly,facebook/folly,facebook/folly,facebook/folly,facebook/folly