Upgrade GCC version to latest

[akbertram]

Renjin currently depends on GCC 4.7, which is now quite old. PR #505 is ready for upgrading to 4.8, but it would be a nice project to upgrade to the latest GCC 11, especially since the plugin API seems to have improved.

Here is an example for GCC 5 which uses the new C++ API:
https://github.com/rofirrim/gcc-plugins

[perNyfelt]

Hi Alex,

Perhaps you could consider merging the 4.8 patch as a first step?
I know the plan was to wait until after 3.5 but there are some enhancements that needs to be done to the gcc bridge to allow us to compile/convert some of the packages that we agreed should make up a "minimum packages support" for a 3.5 release.

I have been brushing up on my C skills during the past couple of weeks getting ready to be able to tackle the gcc bridge enhancement needed but from my point of view, moving to 4.8 now rather later would be preferable.