Strip -Wstrict-prototypes from C++ cython extensions

[isuruf]

In conda, -Wstrict-prototypes is added to CFLAGS and therefore Cython C extensions are compiled with it. These flags are recorded and when a Cython C++ extension depends on C extension, these flags are used resulting a warning.

(C flags like -std=c99 is already stripped from C++ extensions, which means there is already infrastructure to do this.)

Component: build

Issue created by migration from https://trac.sagemath.org/ticket/28093

[jdemeyer]

comment:1

Duplicate of #25316

[jdemeyer]

Replying to @isuruf:

C flags like -std=c99 is already stripped from C++ extensions, which means there is already infrastructure to do this.

Unfortunately, this is not true. The flag -std=c99 is handled by Sage, so we can easily choose whether to add it or not. The flag -Wstrict-prototypes on the other hand is added by distutils itself, it's non-trivial to not add that flag.

I should also add that this has been fixed upstream in Python 3.6, but it looks like it won't be backported to 2.7.