Fix warning about ADEPT_THREAD_LOCAL being redefined in Xcode 13.2.1

[yairchu]

I get the following warning when building in Xcode 13.2.1:

The change avoids redefining and undefining macros with an #else clause.

[rjhogan]

Thanks! However, this won't compile if __has_feature is not available because the preprocessor evaluates both sides of the && regardless of the result of the first test (unlike in the C language). Could you please use a nested #if/#ifdef like in my original code?

[yairchu]

Oh, good to know! So that explains why it was this way. So I'll do an #ifndef ADEPT_THREAD_LOCAL after the nested condition to avoid the two else clauses.

[yairchu]

Fixed

[rjhogan]

Thanks!