A release candidate for GCC 7.4 is available from
ftp://gcc.gnu.org/pub/gcc/snapshots/7.4.0-RC-20181129/ and shortly its mirrors. It has been generated from SVN revision 266611. I have so far bootstrapped and tested the release candidate on x86_64-unknown-linux-gnu. Please test it and report any issues to bugzilla. If all goes well I'd like to release GCC 7.4 at the end of next week.