If users set CMAKE_C_COMPILER or CMAKE_CXX_COMPILER when invoking CMake, the specified compilers will be used to compile the driver, but not to compile external dependencies like EP_mnmlstc_core.

See the attached build log. Note that the user's CMake configure check says "Check for working CXX compiler: /opt/mongodbtoolchain/v2/bin/g++", but the EP_mnmlstc_core configure check says "Check for working CXX compiler: /usr/bin/c++".

Users can use the CC and CXX environment variables to work around this issue.