Maybe there are tradeoffs or platforms I'm just not aware of, but I at least tend to use C99 as the LCD.

At least VS now supports most of C99. Most. Now about that C11...

C11 would be really nice to see as an LCD, especially for threading (or even just a native POSIX threads implementation).

Why would you want that? Autotools is the devil we know. CMake has its own problems and from a statistical sample of one project implementing both, I came to the conclusion that CMake is more frustrating than Autotools when you need to do something unusual.

Those who do not understand autotools are doomed to reinvent it, poorly.

...and it cannot deal with non-exotic use cases like non-UNIX environments (think Windows + Visual Studio) well at all. In contrast, with CMake you can generate an nmake file or Visual Studio project with one command.

It is for that reason I much prefer autotools, especially at the distribution level where you really don't want to be patching things. CMake can work, but I have had to do more patching for CMake build systems than I have had to for autotools; on that basis I consider autotools "better", at least for our use case.

Unusual in terms of...? If I have learnt anything from Go, Java (per Maven), etc. it's that the far majority of project don't need to do something unusual.

Conversely, if you give people the room to do unusual things, they will.

There's a certain simplicity from the perspective of the user that configure && make && make install works most of the time.

CMake requires a lot of effort to get running by comparison.