[mlir] use STATUS instead of CHECK_* in MLIRDetectPythonEnv.cmake

CHECK_* directives for message() where added in Cmake 3.17, LLVM
requires 3.14 as minimum so they may not be intepreted correctly and
just print "CHECK_*" into the message stream. Replace them with STATUS.

Reviewed By: stellaraccident

Differential Revision: https://reviews.llvm.org/D91959