FIPS SLI revamp: __thread check is sensitive to compiler flags

[NIIBE Yutaka]

Lucas Mulling wrote:
> We were backporting FIPS SLI changes to 1.10.3, in our target environment
> `-Wall` and -`Werror=unused-variable` are set, making the check for
> `__thread` fail. FYI if anyone else has this problem, fix attached.

Thank you for your feedback.  Fixed in master by the commit:

	42e8858566e32080aaf818b168f34c698a9ef084

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