[hack] define_globals should not write to shared mem
[hack] define_globals should not write to shared mem

Summary:
There are two main reasons why `define_globals` should not write to the shared memory

1. It is called once by the master process and once by each of the workers. It defines the local globals, but it does NOT initialize the shared memory
2. The memory isn't actually ready to be written yet on Windows.

`init_shared_globals` is the right place for this kind of code.
Closes https://github.com/facebook/flow/pull/2873

Reviewed By: dabek

Differential Revision: D4220440

Pulled By: gabelevi

fbshipit-source-id: d52f25467b77a19178542a002a0b0475392ddcf0

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