Closes Homebrew/homebrew#50537.

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

Don't use ensure to do the final check because it won't affect the
return value of the overall function.

Thanks to @xucheng for catching this bug.

Closes Homebrew/homebrew#50536.

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

SDK 10.10 isn't something that exists for Xcode 7, so stop looking for
it and rely on MACOSX_DEPLOYMENT_TARGET instead.

See PR Homebrew/homebrew#50137 Yosemite build failure

Closes Homebrew/homebrew#50355.

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

This reverts commit 8c7f3d859e8f715b6c63e4fe75e7a636aee4167f.

Closes Homebrew/homebrew#50154.

cf. Homebrew/homebrew#50154

Resolves an issue where xcode-select output with a terminal slash leads
to superenv failing to strip system library paths from ccld-style
invocations.

Fixes Homebrew/homebrew#49731. Discussion in Homebrew/homebrew#50154.

The current approach of suppressing all output regardless of what the
error is makes it very hard to debug any issues and misread but valid
Mach-O files will be silently interpreted as non-Mach-O files instead.

Prefer to fail if we are a Homebrew developer or running on the bot
(`HOMEBREW_DEVELOPER=1`), so that problems will be noticed and fixed
before the silent failure leads to hard-to-diagnose user problems.

Closes Homebrew/homebrew#48817.

Signed-off-by: Martin Afanasjew <martin@afanasjew.de>