Getting the error "/usr/lib64/libstdc++.so.6: version `GLIBCXX_3.4.14' not found" and other errors when I type gmake in Qt directory

I installed the offline installer "Qt 5.8.0 for Linux 64-bit (766 MB)" and also the tar.gz file for Linux and mac users from the following link:

The tar.gz file I downloaded was qt-everywhere-opensource-src-5.8.0.tar

(My system in RHEL 6.6).

I then transferred both the tar.gz file and the installer to my Desktop and I began referring to this link for additional instructions:

On my desktop, I typed these commands:

gunzip qt-everywhere-opensource-src-5.8.0.tar.gz
tar xvf qt-everywhere-opensource-src-5.8.0.tar 

This created the directory qt-everywhere-opensource-src-5.8.0. I then used cd to go inside this directory and I typed ./configure.

Upon this, I was first asked if I wanted the Open-Source edition or the Commercial one and I chose the Open-Source edition. I was then asked if I agreed with the GPL and LGPL licenses and I chose yes again. In the very end I was shown this message:

Qt is now configured for building. Just run 'gmake'.
Once everything is built, you must run 'gmake install'.
Qt will be installed into /usr/local/Qt-5.8.0
Prior to reconfiguration, make sure you remove any leftovers from
the previous build.

After reading this, I wrote gmake on the command line. After processing gmake for several hours, I got these erros:

gmake[4]: Entering directory `/root/Desktop/qt-everywhere-opensource-src-5.8.0/qtscxml/examples/scxml/trafficlight-widgets-static'
/root/Desktop/qt-everywhere-opensource-src-5.8.0/qtscxml/examples/scxml/trafficlight-widgets-static/qscxmlc_wrapper.sh ../trafficlight-common/statemachine.scxml --header statemachine.h --impl ./statemachine.cpp
/root/Desktop/qt-everywhere-opensource-src-5.8.0/qtscxml/bin/qscxmlc: /usr/lib64/libstdc++.so.6: version `GLIBCXX_3.4.14' not found (required by /root/Desktop/qt-everywhere-opensource-src-5.8.0/qtscxml/bin/qscxmlc)
gmake[4]: *** [statemachine.h] Error 1
gmake[4]: Leaving directory `/root/Desktop/qt-everywhere-opensource-src-5.8.0/qtscxml/examples/scxml/trafficlight-widgets-static'
gmake[3]: *** [sub-trafficlight-widgets-static-make_first] Error 2
gmake[3]: Leaving directory `/root/Desktop/qt-everywhere-opensource-src-5.8.0/qtscxml/examples/scxml'
gmake[2]: *** [sub-scxml-make_first] Error 2
gmake[2]: Leaving directory `/root/Desktop/qt-everywhere-opensource-src-5.8.0/qtscxml/examples'
gmake[1]: *** [sub-examples-make_first] Error 2
gmake[1]: Leaving directory `/root/Desktop/qt-everywhere-opensource-src-5.8.0/qtscxml'
gmake: *** [module-qtscxml-make_first] Error 2

Why am I getting these errors? What should I do to resolve them?

EDIT:

When I type gcc -v I get the following output:

Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/root/gcc-4.8.2/libexec/gcc/x86_64-unknown-linux-gnu/4.8.2/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: /root/Downloads/objdir/../gcc-4.8.2/configure --prefix=/root/gcc-4.8.2 --enable-languages=c,c++,fortran,go --disable-multilib
Thread model: posix
gcc version 4.8.2 (GCC) 

I read the errors carefully and realized that the root of my errors is this line:

/root/Desktop/qt-everywhere-opensource-src-5.8.0/qtscxml/bin/qscxmlc: /usr/lib64/libstdc++.so.6: version `GLIBCXX_3.4.14' not found (required by /root/Desktop/qt-everywhere-opensource-src-5.8.0/qtscxml/bin/qscxmlc)

I referred to a Stack Overflow answer and based on that I typed the following command:

strings /usr/lib64/libstdc++.so.6 | grep GLIBCXX and it gave me the following output:

GLIBCXX_3.4
GLIBCXX_3.4.1
GLIBCXX_3.4.2
GLIBCXX_3.4.3
GLIBCXX_3.4.4
GLIBCXX_3.4.5
GLIBCXX_3.4.6
GLIBCXX_3.4.7
GLIBCXX_3.4.8
GLIBCXX_3.4.9
GLIBCXX_3.4.10
GLIBCXX_3.4.11
GLIBCXX_3.4.12
GLIBCXX_3.4.13
GLIBCXX_FORCE_NEW
GLIBCXX_DEBUG_MESSAGE_LENGTH

So apparently, GLIBCXX_3.4.14 isn't on my system and it is looking for it. How can I get around this problem?

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