is there any issue with installing the compat-gcc34 package from CentOS 6 on CentOS 7 ?
probably won’t work at all, as its dependencies are very likely to be all wrong.
compat packages in RHEL/CentOS are designed to go back one major release. So, compat-gcc34 on EL6 was designed for EL5
compatibility. on EL7, there’s a compat-gcc-44 to provide EL6
I suggest you recompile whatever software depends on gcc 3.4 to run with el7’s native gcc 4.8