Auto merge of #38128 - cardoe:req-cmake-only-for-llvm, r=alexcrichton
Auto merge of #38128 - cardoe:req-cmake-only-for-llvm, r=alexcrichton

configure: only req CMake if we're building LLVM

CMake is only necessary if LLVM is going to be built and not in any
other case.

Signed-off-by: Doug Goldstein <8172f793ca553050868d487fd13b508d19cae503@cardoe.com>

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