For example: sccache Where Mozilla is actively pouring in money to make it support firefox-scale builds for each check-in. (Both are recommended reading, Mozilla's own Bazel plans are briefly mentioned!)
Also, cargo is being overhauled for better integration with build tools. Currently they're working on making cargo emit a build plan for other build tools to consume/parallelize/speed-up.
Also, Bazel doesn't "solve" the build time problem, it makes a granularity choice for chunks over the network. That is still a choice, just a different one than rustc is currently making (but as I've linked, distributed build support is being worked on!)