> Necessary to bootstrap GCC. GCC 5.4 or newer has sufficient support for used C++14 features.
> Versions of GCC prior to 15 allow bootstrapping with an ISO C++11 compiler, versions prior to 10.5 allow bootstrapping with an ISO C++98 compiler, and versions prior to 4.8 allow bootstrapping with an ISO C89 compiler.
> If you need to build an intermediate version of GCC in order to bootstrap current GCC, consider GCC 9.5: it can build the current D compiler, and was also the version that declared C++17 support stable.
https://gcc.gnu.org/install/prerequisites.html
So yeah, if you want to enjoy GCC 4.8...
Now I can bother to show exactly each source file, but Github search is relatively easy to use on the mirror source code.