[yuhong]

Yes, they can use a 32-bit cl.exe and 64-bit linker, but most build systems don't make it easy.

[bzbarsky]

You can't use a 32-bit cl.exe and a 64-bit linker to produce 32-bit binaries if you're doing PGO (which is the whole point of this "using lots of memory" issue). In particular, the 64-bit linker can't produce 32-bit binaries when you're using link-time code generation, which PGO does.