setup: relax -Werror for declaration-after-statement on Python 3.9
It turns out Python 3.9 introduces such declarations in the headers, eg
cpython/abstract.h:189:5: error: ISO C90 forbids mixed declarations and code [-Werror=declaration-after-statement]
so we have to be more relaxed when compiling for 3.9.
Differential Revision: https://phab.mercurial-scm.org/D8327
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- Regex: '^<'
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- Regex: '^"'
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