[Dlang-internal] make std/algorithm/comparison.test should only test that module

[Andrei Alexandrescu]

Hi, per posix.mak:

# make std/somemodule.test => only builds and unittests std.somemodule

I just tried:

make std/algorithm/comparison.test

and it seems to build and run all tests. Before I look into it closer, 
any known change that affected this? Thanks.