folly Symbolizer: fix destruction-order fiasco problem
folly Symbolizer: fix destruction-order fiasco problem

Summary: On a (broken) unit test there is a bad `CHECK` during destruction time.  This triggers an ABRT, goes through the signal handler, and in the process ends up doing a use-after-free.

Moved some globals inside the functions in which they are used (w/ little duplication, as they are used in one place, mostly).

Reviewed By: @luciang, @meyering

Differential Revision: D2494046

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