CentOS 8 already comes with GCC 8.

On CentOS 7, you can install GCC 8 from Developer Toolset. First you need to enable the Software Collections repository:

yum install centos-release-scl

Then you can install GCC 8 and its C++ compiler:

yum install devtoolset-8-gcc devtoolset-8-gcc-c++

To switch to a shell which defaults gcc and g++ to this GCC version, use:

scl enable devtoolset-8 -- bash

You need to wrap all commands under the scl call, so that the process environment changes performed by this command affect all subshells. For example, you could use the scl command to invoke a shell script that performs the required actions.

From the appropriate bug report:

Jakub Jelinek 2017-05-13 06:52:08 UTC

The bug is on the GCC 4.8 side, so either you need to patch it, or build with -std=gnu++98 - then __GNUC_STDC_INLINE__ will not be defined and it ought to compile fine.

Please check this answer as well: https://unix.stackexchange.com/a/472713/260833

If you wish to install an older gcc than the distro provides, you will need to compile it for source.

There is some guidance below on how to download and build an old GCC

https://bytefreaks.net/gnulinux/downgrade-gcc-on-centos-7-0-64bit-to-version-4-8-2

You can only downgrade to the version already offered by CentOS 8 and GCC 6.3.1 doesn't fit the bill.

Unfortunately the only way to install this version of GCC without wreaking havoc to your system is to download the source, compile and install it into e.g. /opt/gcc6

As for compile flags check Fedora or CentOS src.rpms - you'll only need to add --prefix=/opt/gcc6

Update: here's how I compiled GCC 4-7:

Unpack it.

(under root/sudo) yum install gcc make glibc-devel gmp-devel mpfr-devel gmp-devel

export CFLAGS="-O2 -march=native -pipe"
export CXXFLAGS=$CFLAGS
cd gcc-6.3.1
mkdir BUILD
cd BUILD

../configure --enable-shared --enable-threads=posix --disable-stage1-checking \
--with-system-zlib --enable-__cxa_atexit --enable-multilib --with-gnu-as \
--with-gnu-ld --enable-languages="c,c++" --without-x --prefix=/opt/gcc \
--disable-libunwind-exceptions --with-gmp=/usr

Simply use dnf

Copydnf -y install gcc-toolset-9-gcc gcc-toolset-9-gcc-c++
source /opt/rh/gcc-toolset-9/enable

ref: https://centos.pkgs.org/8/centos-appstream-x86_64/gcc-toolset-9-gcc-9.1.1-2.4.el8.x86_64.rpm.html

Note: source won't work inside a Dockerfile so prefer to use:

CopyENV PATH=/opt/rh/gcc-toolset-9/root/usr/bin:$PATH

or better

CopyRUN dnf -y install gcc-toolset-9-gcc gcc-toolset-9-gcc-c++

RUN echo "source /opt/rh/gcc-toolset-9/enable" >> /etc/bashrc
SHELL ["/bin/bash", "--login", "-c"]
RUN gcc --version

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.