solver: parse cabal errors also on Windows
solver: parse cabal errors also on Windows

As shown in #2502, `cabal init --solver` can fail with `Could not parse
cabal-install errors` on Windows.  The problem boils down to the fact that
we test `isSuffixOf "suffix" "stuff suffix\r"`, which is false, so we
should better strip `\r` before calling `isSuffixOf`.

I've verified that `\r` is actually there only indirectly; I inferred it
from the presence of `stripCR` and the parse failure, and I've recently
seen the behavior of lines on strings with Windows line ends.

Testing confirms this PR fixes the bug—the original procedure fails with
the parent commit and works with this one.

juhp/stack,juhp/stack,Fuuzetsu/stack,Fuuzetsu/stack,mrkkrp/stack,martin-kolinek/stack,AndrewRademacher/stack,MichielDerhaeg/stack,AndrewRademacher/stack,MichielDerhaeg/stack,deech/stack,mrkkrp/stack,AndreasPK/stack,deech/stack,martin-kolinek/stack,AndreasPK/stack,anton-dessiatov/stack,anton-dessiatov/stack