Remove -march=native from default flags

[Luthaf]

This is broken in multiple ways right now: #383, #335. I also got a different error when trying to build librascal on a fresh M1 install (macOS Monterey):

-- The C compiler identification is AppleClang 13.1.6.13160021
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: /Library/Developer/CommandLineTools/usr/bin/cc - skipped
-- Detecting C compile features
-- Detecting C compile features - done
-- The CXX compiler identification is AppleClang 13.1.6.13160021
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /Library/Developer/CommandLineTools/usr/bin/c++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Configuring done
-- Generating done
-- Build files have been written to: /Users/guillaume/code/librascal/_cmake_test_compile/build
-- Build type is: Release
-- The CXX compiler identification is AppleClang 13.1.6.13160021
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /Library/Developer/CommandLineTools/usr/bin/c++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Downloading wigxjpf
-- Downloading Eigen3
-- Eigen3 3.3.4
-- Found PythonInterp: /Users/guillaume/code/librascal/virtualenv/bin/python (found suitable version "3.10", minimum required is "3")
-- Found PythonLibs: /opt/miniforge3/lib/libpython3.10.dylib
-- Downloading pybind11
-- pybind11 v2.3.0
-- Installation ROOT: /Users/guillaume/code/librascal/_skbuild/macosx-12.0-arm64-3.10/cmake-install
-- The project is built using scikit-build
-- The optional cpplint parser has not been found. For more information see https://pypi.python.org/pypi/cpplint
-- clang-format not found, so the pretty-cpp target is unavailable
-- BLACK auto formatter: /opt/miniforge3/bin/black
-- Configuring done
-- Generating done
-- Build files have been written to: /Users/guillaume/code/librascal/_skbuild/macosx-12.0-arm64-3.10/cmake-build
[1/20] Building CXX object src/CMakeFiles/rascal.dir/rascal/utils/json_io.cc.o
FAILED: src/CMakeFiles/rascal.dir/rascal/utils/json_io.cc.o
/Library/Developer/CommandLineTools/usr/bin/c++ -Drascal_EXPORTS -I/Users/guillaume/code/librascal/src -isystem /Users/guillaume/code/librascal/_skbuild/macosx-12.0-arm64-3.10/cmake-build/external/Eigen3 -isystem /Users/guillaume/code/librascal/_skbuild/macosx-12.0-arm64-3.10/cmake-build/external/wigxjpf/inc -isystem /Users/guillaume/code/librascal/_skbuild/macosx-12.0-arm64-3.10/cmake-build/external/wigxjpf/cfg -Wall -Wextra -Weffc++ -Wno-non-virtual-dtor -O3 -DNDEBUG -march=native -arch arm64 -isysroot /Library/Developer/CommandLineTools/SDKs/MacOSX12.3.sdk -mmacosx-version-min=12.0 -fPIC -Werror -std=gnu++14 -MD -MT src/CMakeFiles/rascal.dir/rascal/utils/json_io.cc.o -MF src/CMakeFiles/rascal.dir/rascal/utils/json_io.cc.o.d -o src/CMakeFiles/rascal.dir/rascal/utils/json_io.cc.o -c /Users/guillaume/code/librascal/src/rascal/utils/json_io.cc
clang: error: the clang compiler does not support '-march=native'

Users who want to use -march=native can still specify it in CMAKE_CXX_FLAGS and get any corresponding benefits.

[agoscinski]

Should we add march at least to the default pip installation?

librascal/setup.py

Line 31 in 9a9fbdc

cmake_args=[

Since march seems to potentially give speed ups for numerical code by enabling SSE 2 > instructions.
https://stackoverflow.com/a/52660117

[Luthaf]

No, because this would also fail when compiling the python binding on M1 CPU.

If someone wants to put in the time to figure out a robust way to add back -march=native without breaking some platforms, we can do it later, but I would rather have something which works for now.

[agoscinski]

fair enough