I just compiled some C++ code using G++ under ulimit -v 108032, but it didn't use much of the STL. For a simple example program using iostream, vector, unique_ptr, and std::string, I needed more, but had success with ulimit -v 262144: http://canonical.org/~kragen/sw/dev3/docentes.cc.

The last "real" C++ code I wrote was probably the modular softsynth in http://canonical.org/~kragen/sw/dev3/sweetdreams-c++.cc (see http://canonical.org/~kragen/sw/dev3/sweetdreams.html for an explanation) which also compiles successfully in under 256MiB of virtual memory (¼GiB). But that's still under 500 lines of code.

I'm not sure how much RAM you need to compile G++ itself. More, I imagine. I was definitely compiling versions of GCC long before I ever saw a machine with so much RAM as 1GB, but I am guessing you probably need at least 1GiB for recent versions, maybe 4GiB.

LLVM, which is required for both clang and Rust, is much heavier. You definitely can't compile current versions of LLVM on i386, m68k, or any 32-bit platform anymore. You can get it to cross-compile to them as targets. In theory there are PPC64 machines that have enough address space to build it, but I'm not sure anyone ever made a PPC64 machine with enough physical RAM to build it in a practical span of time.

I run OpenBSD 7.8 under an i386 ATOM netbook, n270 CPU and 1GB of RAM. I hav no Rust, but I have C++, JimTCL, nim (I compled Chawan). Go runs, too. Maybe I can't compile LLVM in my netbook, but a tuned up machine with 2-4GB of RAM might be able to do such task with a bit of swap in a SSD and boosted up login.conf limits.