rustbuild: Sanity-check cmake for sanitizers too
rustbuild: Sanity-check cmake for sanitizers too

It's possible to build the sanitizers when using an external LLVM, but
we still need cmake for this.  Extend the sanity check to look for cmake
whenever sanitizers are enabled too.

GBGamer/rust,aidancully/rust,GBGamer/rust,graydon/rust,GBGamer/rust,graydon/rust,GBGamer/rust,aidancully/rust,graydon/rust,aidancully/rust,aidancully/rust,GBGamer/rust,graydon/rust,graydon/rust,GBGamer/rust,graydon/rust,GBGamer/rust,aidancully/rust,aidancully/rust,GBGamer/rust