link executables dynamically to speed up linking

[develop7]

Dramatically decreases linking times and shaves 6 of 14G off HLS' dist-newstyle directory on my machine by producing way smaller executables.

While cabal building HLS after switching a branch I've noticed linking test executables takes minutes, plural, each. Then I've checked the size of a freshly-built test binary and it was 150-something megabytes, no wonder linker took a while. With executable-dynamic enabled, linking is lightning fast and binaries are a megabyte at most, which should probably improve the developer experience and decrease the feedback loop time.

UPD: https://github.com/haskell/haskell-language-server/issues/2659 seems related, not sure how up-to-date though