Something like: `make check-c++ RUNTESTFLAGS=modules.exp=depflags-f*`
Where `modules.exp` is the .exp file in the dir that contains the specific test files to test. (Edit: used `check-c++` instead of `check` which narrows things down to only the C++ tests ... which I think is implied by `modules.exp` anyway, but I'm not sure.) -- https://forge.sourceware.org/gcc/gcc-TEST/pulls/134#issuecomment-4889
