When using the build invocation:
python3.8 buildscripts/scons.py --variables-files=etc/scons/mongodbtoolchain_stable_clang.vars --gcov
The build will fail with this error:
Checking if C compiler is clang 7.0 (or Apple XCode 10.2) or newer...no Checking if C++ compiler is clang 7.0 (or Apple XCode 10.2) or newer...no ERROR: Refusing to build with compiler that does not meet requirements See /home/ubuntu/mongo/build/scons/config.log for details
The build could check if the gcov option is being used with clang, and report that clang and --gcov is not currently supported, and alternatively use --gcov with gcc instead.