I'd recommend using yum localinstall rather than using the rpm command directly; that way you'll have the gcc package in your yum database so that it can keep track of updates. The command would just be:

yum localinstall /mnt/cdrom/CentOS/gcc-(whatever).rpm

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.

Tru Huynh of centos.org has built the redhat developer toolset 1.1, for centos and it contains gcc 4.7.2

So you could simply use his repo and install just gcc, instantly.

cd /etc/yum.repos.d
wget http://people.centos.org/tru/devtools-1.1/devtools-1.1.repo 
yum --enablerepo=testing-1.1-devtools-6 install devtoolset-1.1-gcc devtoolset-1.1-gcc-c++

This will install it most likely into /opt/centos/devtoolset-1.1/root/usr/bin/

Then you can tell your compile process to use the gcc 4.7 instead of 4.4 with the CC variable

export CC=/opt/centos/devtoolset-1.1/root/usr/bin/gcc  
export CPP=/opt/centos/devtoolset-1.1/root/usr/bin/cpp
export CXX=/opt/centos/devtoolset-1.1/root/usr/bin/c++