I think I found just what I needed. Somehow I overlooked it before. Right there on Erik Anderson’s uClibc page, near the bottom, there’s his uClibc development environment. What is it? A Linux distribution based on his uClibc, busybox and tinylogin userspace in addition to enough GNU tools to compile other stuff. If you don’t want all 150 megs’ worth, download his makefile and uncomment just the stuff you want.
It’s not a general-purpose Linux distribution. It’s intended as a development environment. But besides that, it would be perfect for running on a low-end PC, like a 386 or 486 laptop. You get the benefits of a modern kernel and a modern, in-development libc, but with everything designed to lower memory consumption. On an older PC with a slow hard disk, that all translates into better performance.
Now I’m not sure how much of a GUI you get, but frankly, an older laptop, especially a network-capable one, with this stuff and the excellent Links web browser, the machine would be useful. If SVGAlib and the SVGAlib-capable version of Links compile, then you could even have a graphical web browser on a low-octane machine. Wouldn’t that be cool?