BUG: numpy build fails with gcc version 4.9.2

[jzombi]

Describe the issue:

Numpy fails to build with gcc version 4.9.2 with the following error:

RuntimeError: Broken toolchain: cannot link a simple C++ program. note: A compiler with support for C++11 language features is required.

This should not be a problem, because C++11 standard is supported since gcc 4.8.1.

The problem is that when compiling the test code in numpy/core/setup.py, the -std=c++11 flag is not passed to the compiler.
The default c++ standard was changed in version 6.1 from C++98 to C++14, so this issue might affect all prior gcc versions.

By monkey-patching setup.py to include the -std=c++11 flag, the build run successfully.

Reproduce the code example:

python setup.py build

Error message:

RuntimeError: Broken toolchain: cannot link a simple C++ program. note: A compiler with support for C++11 language features is required.

NumPy/Python version information:

1.22.3 3.8.12 (default, Jan 12 2022, 09:59:17)
[GCC 4.9.2]

[seberg]

@serge-sans-paille should we be adding this flag (on old gccs?)

[mattip]

See also #20344 which tried to enable -std=c++11 only where required. We had a gcc 4.8 run in CI but dropped it in #19665, with a comment about maybe restoring it if we get pushback. It seems there is at least one user still compiling with an older gcc, maybe we should reconsider the CI run.

[serge-sans-paille]

The problem is that when compiling the test code in numpy/core/setup.py, the -std=c++11 flag is not passed to the compiler.

This is strange, because we're passing -std=c++11 to extra_cxx_compile_args= in both numpy/linalg/setup.py and numpy/core/setup.py

[serge-sans-paille]

#21306 should fix the issue

[jzombi]

@serge-sans-paille it works, thanks!
(I leave this issue open, because it seems that when your commit is merged in main, it will be automatically closed.)