I tried to compile Python 3.9 with:


CC=gcc-9.2.0  ./configure --enable-optimizations --with-lto --with-cxx-main=g++-9.2.0
make -j 2

I got this error:

g++-9.2.0 -c -Wno-unused-result -Wsign-compare -DNDEBUG -g -fwrapv -O3 -Wall    -flto -fuse-linker-plugin -ffat-lto-objects -flto-partition=none -g -std=c99 -Wextra -Wno-unused-result -Wno-unused-parameter -Wno-missing-field-initializers -Werror=implicit-function-declaration -fvisibility=hidden -fprofile-generate -I./Include/internal  -I. -I./Include    -DPy_BUILD_CORE -o Programs/_testembed.o ./Programs/_testembed.c
cc1plus: warning: ‘-Werror=’ argument ‘-Werror=implicit-function-declaration’ is not valid for C++
cc1plus: warning: command line option ‘-std=c99’ is valid for C/ObjC but not for C++
sed -e "s,@EXENAME@,/usr/local/bin/python3.9," < ./Misc/python-config.in >python-config.py
LC_ALL=C sed -e 's,\$(\([A-Za-z0-9_]*\)),\$\{\1\},g' < Misc/python-config.sh >python-config
gcc-9.2.0 -pthread -c -Wno-unused-result -Wsign-compare -DNDEBUG -g -fwrapv -O3 -Wall    -flto -fuse-linker-plugin -ffat-lto-objects -flto-partition=none -g -std=c99 -Wextra -Wno-unused-result -Wno-unused-parameter -Wno-missing-field-initializers -Werror=implicit-function-declaration -fvisibility=hidden -fprofile-generate -I./Include/internal  -I. -I./Include    -DPy_BUILD_CORE \
      -DGITVERSION="\"`LC_ALL=C git --git-dir ./.git rev-parse --short HEAD`\"" \
      -DGITTAG="\"`LC_ALL=C git --git-dir ./.git describe --all --always --dirty`\"" \
      -DGITBRANCH="\"`LC_ALL=C git --git-dir ./.git name-rev --name-only HEAD`\"" \
      -o Modules/getbuildinfo.o ./Modules/getbuildinfo.c
In file included from ./Include/internal/pycore_atomic.h:15,
                 from ./Include/internal/pycore_gil.h:11,
                 from ./Include/internal/pycore_pystate.h:11,
                 from ./Programs/_testembed.c:10:
/usr/local/lib/gcc/x86_64-pc-linux-gnu/9.2.0/include/stdatomic.h:40:9: error: ‘_Atomic’ does not name a type

I suppose simply `Programs/_testembed.c` is a C source file and must not be compiled with g++

PS: as a workaround, `--with-cxx-main=gcc-9.2.0` works, but probably it's not optimal.