Some of these tests instruct the RTS to ignore all RTS flags being
passed.  While this is intended it causes test failures for some ways
like profiling which depend on passing RTS flags. So we skip these ways.

Test Plan: testsuite/tests/rts/flags$ make slow

Reviewers: bgamari, simonmar, alpmestan

Reviewed By: alpmestan

Subscribers: alpmestan, thomie, carter

GHC Trac Issues: #12870

Differential Revision: https://phabricator.haskell.org/D4585