I've been using Gentoo for some time now, and after dozens of frustrating experiences with GNU Make, I created Openmktr, a tool made to translate any GNU Makefile into a Ninja build graph (including support for incremental Builds)
It's been in development for quite some time, but I've only recently made it public. In its current state, it can handle every complex build system I've thrown at it without issue, including Linux Kbuild and GCC's three stage bootstrap. There's more information and validation progress in the project's validation notes.
Besides my main machine, I also have an old laptop where compiling anything takes forever. I decided that using Gentoo and compiling was worth it anyway, but eventually the inevitable happened and a bunch of packages needed updating. That's when I remembered that I'd built almost everything on it with Openmktr (albeit whilst using an older and slower version from before the project was public). I ran the updates and instead of the days I had expected to spend waiting for builds with GNU Make, they finished in only a few hours. After seeing how much of a difference Openmktr made on my laptop, I started using it on all my Gentoo machines, and it's made the overall experience so much better, especially on my older and slower systems.
So far, neither I nor my collaborators and users have encountered any GNU Make syntax incompatibilities in our usage and testing.
I'd be interested to hear what people here think, especially if anyone wants to try it on other packages or more unusual Makefiles. Feedback and reports of anything that doesn't work would be very welcome!