Two changes:

  * strip static libraries (.a files) at install/copy time, instead of
    at build time. Note that Cabal strips shared libraries (.so files)
    and executables at install/copy time also.

    This is needed for GHC, because it uses Cabal (via ghc-cabal copy)
    to install the boot libraries, and relies on Cabal to take of
    library stripping. Currently .so files indeed get properly stripped,
    but .a files do not.

    (Stripping static libraries at build time was introduced in
    60409cb9, with the explanation:
    "Call 'stripLib' from createLibArchive so that it's done only
    once.")

    This bug (if you want to call it that) partially explains the
    difference in size of a GHC installation before and after manual
    stripping, reported in
    https://github.com/haskell/cabal/issues/1622#issuecomment-62076817
    (The other parts are that the GHC build system currently doesn't
    strip executables on installation:
    https://ghc.haskell.org/trac/ghc/ticket/9087, and neither are the
    RTS library stripped, since they don't go through Cabal).

  * never strip the copy of a library in the build directory. Only
    strip the copy that is installed. Note that Cabal never strips
    executables in the build directory either.

    This might speed up compilation of a package under development,
    since stripping won't be performed for every 'cabal build'. It is
    also consistent with the GNU coding standards for 'install-strip':

      "install-strip should not strip the executables in the build
      directory which are being copied for installation. It should only
      strip the copies that are installed."

    Source:
    http://www.gnu.org/prep/standards/html_node/Standard-Targets.html