This unifies the logic for selecting a compiler between superenv and
stdenv. A variation of superenv's `determine_cc`, which now returns a
symbol, has been moved into the shared ENV extension. Stdenv uses the
result of this directly (as it's always used symbols), while superenv
translates that back into a compiler string.

This also has the effect of disabling HOMEBREW_USE_(gcc|llvm|clang) in
stdenv, which have already been marked as deprecated for some time, and
enables the HOMEBREW_CC= environment variable syntax from superenv in
stdenv.

Closes Homebrew/homebrew#22210.

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

Closes Homebrew/homebrew#22138.

Closes Homebrew/homebrew#22202.

This allows overriding the "oldest CPU" behaviour - for instance, to
build Intel bottles for a newer CPU than Core 2, to build a PPC bottle
with or without Altivec on the same computer, etc.

On PPC, -mcpu is the preferred equivalent to -march.

Otherwiese a `Cellar/.DS_Store` may lead to an error about
`.ds_store.rb` not found during `brew upgrade`.

This reverts commit dca89db55189a34f1c02d3f12a84eda8d81fd6d1.

This sets cpp to use the compiler as cpp, and works with scripts which
pass values to cpp on stdin as well as with file arguments.

Closes Homebrew/homebrew#22155.

An issue could arise when brewing a formula that
has Python 2.x and 3.x support and 2.x is the system Python
but 3.x is a brewed one. The idea about prepending was that
user configured PYTHONPATH could be used in formulae.
Now, instead and if needed, inside the `python do` block
one can still append to PYTHONPATH.

If `depends_on :python => ['modulename', :optional]` then the generated
option is now `--with-python-modulename`, so that it is possible to
actually make depending on python modules optional.
Further, `brew options` becomes more meaningful.

Allows for building bottles on PPC both with and without Altivec.
This is currently not active but will be enabled once superenv is
stable on Leopard.

Fixes Homebrew/homebrew#22090.

When a formula `depends_on :python` *and* `depends_on :python3`
the `modify_build_environment` method sets the PYTHONPATH
and the Python 3.x requirement then fails because it finds
the sitecustomize.py from Python 2.x in the PYTHONPATH.

We use install_name_tool pretty liberally, so we need to take steps to
ensure libraries and executables are always linked with this flag.

Closes Homebrew/homebrew#20233.
Fixes Homebrew/homebrew#17984.
Fixes Homebrew/homebrew#22078.

Closes Homebrew/homebrew#22061.

Signed-off-by: Samuel John <github@SamuelJohn.de>

'gcc' could refer to anything of llvm-gcc, clang, or gcc-4.0 on
various Xcode versions.

Options collections are backed by Sets, and thus trying to push a new
option with a name that duplicates an existing option cannot succeed.

Later, we can exploit this behavior and remove some conditionals.

Closes Homebrew/homebrew#22051.

Signed-off-by: Samuel John <github@SamuelJohn.de>

... and not just installed ones. Of course, strictly speaking,
reinstalling not-yet-installed formulae makes semantically little
sense, but the big win is that we can tell people (after we have
resolved an issue) to `brew reinstall <formula>` and even if a user
has removed that formula in the meantime, reinstall will do the right
thing. Basically adding --force to uninstall. I think this makes
reinstall more robust.

This reverts commit 865f763ae59fdf32f496ca416fd98117f3370f86.

... and not just installed ones. Of course, strictly speaking,
reinstalling not-yet-installed formulae makes semantically little
sense, but the big win is that we can tell people (after we have
resolved an issue) to `brew reinstall <formula>` and even if a user
has removed that formula in the meantime, reinstall will do the right
thing. Basically adding --force to uninstall. I think this makes
reinstall more robust.

A huge cheat sheet. Kind of.