I am using CentOS 7.9 and I encountered the same problem after following instructions here to install and run gcc 11. I tried launching different versions of gcc and found only devtoolset-9 works, which corresponds to the file devtoolset-9 in /etc/scl/conf/ folder. So I copied devtoolset-9 to devtoolset-11 in the same folder, and gcc 11 gets working.

Figured it out. cmake was using an old version of gcc/g++, not the one that my command line was picking up when I ran gcc or g++ myself. So, I had to export CC and CXX to the appropriate paths before running cmake.

export CC=/opt/rh/devtoolset-7/root/usr/bin/gcc
export CXX=/opt/rh/devtoolset-7/root/usr/bin/g++
cmake3 -G "Unix Makefiles" -DCMAKE_BUILD_TYPE=Release ..

Previously, I was only running the last line above.

FROM centos:centos7
RUN yum update -y
RUN yum groupinstall "Development Tools" -y    
RUN yum install wget -y
RUN curl -O https://ftp.gnu.org/gnu/gcc/gcc-7.3.0/gcc-7.3.0.tar.gz
RUN tar xzf gcc-7.3.0.tar.gz
RUN cd gcc-7.3.0
RUN ./contrib/download_prerequisites
RUN cd ..
RUN mkdir gcc-build
RUN cd gcc-build
RUN ../gcc-7.3.0/configure                           \
    --enable-shared                                  \
    --enable-threads=posix                           \
    --enable-__cxa_atexit                            \
    --enable-clocale=gnu                             \
    --disable-multilib                               \
    --enable-languages=all
RUN make
# (Go make a cup of ice tea :)
RUN make install

To save the build time you can create a new docker from the running docker using "docker commit" or save /usr/local to a tar file and open it on any other fresh centos7 docker.

To install the full tools-set including gfortran on centos 7:

yum install centos-release-scl
yum install devtoolset-8
scl enable devtoolset-8 -- bash

enable the tools:

source /opt/rh/devtoolset-8/enable 

you may wish to put the command above in .bash_profile

ref: https://unix.stackexchange.com/questions/477360/centos-7-gcc-8-installation

Now devtools-8 is available and it's possible to use it by following commands:

yum install centos-release-scl
yum install devtoolset-8-gcc devtoolset-8-gcc-c++
scl enable devtoolset-8 -- bash

It's explained in a little more detail in this answer on StackOverflow: How to install GCC/G++ 8 on CentOS. And of course, if you need GFortran, you can install it in the same way - the package is devtoolset-8-gcc-gfortran.

Anyway, the resulting artifacts appear to be linked with system default version of libstdc++:

Yes. The devtoolset-6-gcc-c++ package provides a custom version of GCC that uses a special linker script instead of a dynamic library for libstdc++.so. That means the binaries it produces do not depend on the newer libstdc++.so.6 and can be run on other CentOS machines that don't have devtoolset installed (i.e. they only have the older libstdc++ library from GCC 4.8).

Is this build environment configuration valid?

Yes. What you're seeing is completely normal, and how it's supposed to work.

The pieces of the newer C++ runtime from GCC 6.4.0 get statically linked into your binary, and at runtime it only depends on the old libstdc++.so which every CentOS system has installed.

That's the whole point of the devtoolset version of GCC.