[issue21121] -Werror=declaration-after-statement is added even for extension modules through setup.py

[nils]

New submission from nils:

I got an error while rebuilding a module for 3.4. This was a ISO C90 error but setup.py explicitely adds "-std=c99" to the gcc parameters, and indeed it is used. 

fifo.h:114:5: error: ISO C90 forbids mixed declarations and code [-Werror=declaration-after-statement]
uint32_t ofs = fifo->write_count - fifo->write_offset; 

However, Py 3.4 seems to add -Werror=declaration-after-statement also for extension modules. This should not happe (said also Yhg1s in #python).

Attached is a file that shows the setup.py and also the error log.

----------
components: Build, Distutils, Extension Modules
files: pybug.txt
messages: 215305
nosy: dstufft, eric.araujo, nilsge
priority: normal
severity: normal
status: open
title: -Werror=declaration-after-statement is added even for extension modules through setup.py
versions: Python 3.4
Added file: http://bugs.python.org/file34692/pybug.txt

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<http://bugs.python.org/issue21121>
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