The first release candidate for GCC 8.4 is available from https://gcc.gnu.org/pub/gcc/snapshots/8.4.0-RC-20200226/ ftp://gcc.gnu.org/pub/gcc/snapshots/8.4.0-RC-20200226/
and shortly its mirrors. It has been generated from git commit r8-10091-gf80c40f93f9e8781b14f1a8301467f117fd24051. I have so far bootstrapped and tested the release candidate on x86_64-linux and i686-linux. Please test it and report any issues to bugzilla. If all goes well, I'd like to release 8.4 on Wednesday, March 4th.