I was going to say nothing in the RISC-V world is comparable to the N100 yet, at any price, but it looks like the N100 is anywhere from 10 to 20 times faster than the N270.
Geekbench 6 doesn't have any N270 results but it has a couple of Atom 230 results, and other sources indicate those two are very similar.
So, ok, on Geekbench a single core of the JH7110 comes in a bit faster than the Atom 230. And it's got four of them. You can get a Milk-V Mars CM with a 1.5 GHz JH7110 with 2 GB RAM for $34. You should be able to build a decent little netbook around that for $100. It's compatible with the Raspberry Pi 4 CM, so if there is a suitable netbook enclosure for the Pi 4 CM then it should work.
Otherwise I think the ClockworkPi DevTerm R-01 would be the closest that actually exist at the moment. The single 1.0 GHz C906 core is a bit slower and the price is unfortunately $239.
You can always reduce the number of jobs from make/ninja to 4...
But, yes, you are right; the issue lies on linking. LibTD requires 2GB as minimum, but linking takes ages. At least with GCC, Clang requires far less RAM.
Not everyone needs a 16GB machine to compile huge current C++ projects.