Move some stuff formerly in `Library/ENV` around:
- Move `Library/ENV/$XCODE_VERSION` to `Library/Homebrew/env/super` as they are
  all superenv wrappers and all symlinks to the same version. We never needed
  the "separate shims for separate versions" functionality and it just adds
  confusion.
- Move `Library/ENV/pkgconfig` to `Library/Homebrew/env/pkgconfig` to get more
  things under `Library/Homebrew`
- Move `Library/ENV/scm` to `Library/scm` as these wrappers are not actually
  used by or related to superenv (or stdenv) in any way.

Old logic doesn't include revision. This fixes that, and passes the
whole formula prefix path to avoid duplicating the path-construction
logic.

Closes #80.

Signed-off-by: Andrew Janke <andrew@apjanke.net>

Fixes build error in Homebrew/homebrew-core#100.

Closes #63.

Signed-off-by: Andrew Janke <andrew@apjanke.net>

Closes #32.

Signed-off-by: Misty De Meo <mistydemeo@github.com>

This was intended to filter out MacPorts and X11 paths, but the user
may have valid reasons to have other things here that might get linked
against.

Closes #50425.

Signed-off-by: Misty De Meo <mistydemeo@github.com>

Previously, superenv did not try to filter -I or -L flags
based on the list of requested dependencies; as a result, buildsystems
which opportunistically discover Homebrew-installed libraries were able
to link against them even under superenv.

This adds a list of all requested dependencies to the superenv environment,
and compares all -I and -L flags against those; any Cellar and opt paths
found which resolve to unrequested dependencies are filtered out.

"--fast-math" caused build failure with clang for
homebrew/science/delly-0.7.2

Apparently, clang only likes this option when it's referred to as
"-ffast-math"

Closes Homebrew/homebrew#50507.

Signed-off-by: ilovezfs <ilovezfs@icloud.com>

We cannot really recover from this, but at least we'll provide a clearer
error message than trying to call `exec` with an empty string.