Remove executable filename check on windows

On Windows GHC enforces currently that the real executable is named
ghc.exe/ghc-stage[123].exe.

I don't see a good reason why this is neccessary.
This patch removes this restriction and fixes #14652

Test Plan: ci

Reviewers: bgamari, Phyx

Reviewed By: Phyx

Subscribers: Phyx, rwbarton, thomie, carter

GHC Trac Issues: #14652

Differential Revision: https://phabricator.haskell.org/D4296

(cherry picked from commit 1bf70b20)