Since !6041 (merged), we add a BOM to response files to tell MSVC tooling that they are encoded as UTF-8. However, the "NMake Makefiles" generator may also be used with non-MSVC toolchains that do not understand the BOM. Update the response file encoding selection heuristic to add the BOM only with MSVC tooling.
Fixes: #23143 (closed)
Backport: release