add :osxfuse symbolic dependency
add ConflictsWithFuseForOsx requirement for osxfuse/fuse4x/fuse4x-kext

Closes Homebrew/homebrew#31975.

Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>

This flag was supported in gcc-4.0, but not later GCCs or clang.
It pops up in older python-configs, and may also come up in other
contexts.

Fixes mistydemeo/tigerbrew#213.

Closes Homebrew/homebrew#31384.

Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>

Closes Homebrew/homebrew#30930.

Signed-off-by: Jack Nagel <jacknagel@gmail.com>

Closes Homebrew/homebrew#29795.
Closes Homebrew/homebrew#29819.

'-fno-tree-pre' and '-fno-tree-dominator-opts'

Closes Homebrew/homebrew#29452.

Signed-off-by: Jack Nagel <jacknagel@gmail.com>

I found the dual use of CMAKE_*_PATH variables to make it difficult to
reason about this code. Now a separate set of variables are used to
communicate with the cc wrapper, and less work is performed in the
wrapper itself.

We no longer pass the SDK include path as a -isystem directory on
Xcode-only setups. Doing so is redundant with `--sysroot` and has other
side effects, namely changing the include path search order, which can
break compilation of some software (e.g. qemu).

On Xcode-only 10.9, we can additionally omit `--sysroot`, as the correct
paths are built into the tools.

A new variable, HOMEBREW_SYSROOT, is used to this information to the
wrapper. It will be unset on Xcode-only 10.9. HOMEBREW_SDKROOT will
continue to be set, as it is used for other things besides setting the
include search path.

Closes Homebrew/homebrew#17352.

This reverts commit 61d8a8e029079ca1922df735683c2b5eb6a39db1.

Fixes Homebrew/homebrew#29141.

When the cc wrapper is in cxxld mode, -stdlib= is added by both cxxflags
and ldflags, but they are never used separately, so this results in
duplicate flags.

These flags cannot be used behind -Xarch_<arch>, so stop filtering them
there.

Fixes Homebrew/homebrew#28680.