Build Qt on OS X Command-Line Tools Only.

Currently you cannot build or link into Qt on an OS X Command-Line Tools only machine due to a hard requirement of "xcodebuild" in the code.

Attempting to build from source encounters:

==> ./configure -prefix /usr/local/Cellar/qt5/5.3.2 -system-zlib -qt-libpng -qt-libjpeg -confirm-license -opensource -nomake examples -nomake tests -release -sdk -no-xcb -arch x86_64
+ cd qtbase
+ /private/tmp/qt5-nwIzhu/qt-everywhere-opensource-src-5.3.2/qtbase/configure -top-level -prefix /usr/local/Cellar/qt5/5.3.2 -system-zlib -qt-libpng -qt-libjpeg -confirm-license -opensource -nomake examples -nomake tests -release -sdk -no-xcb -arch x86_64

This is the Qt Open Source Edition.

You are licensed to use this software under the terms of
the Lesser GNU General Public License (LGPL) versions 2.1.
You are also licensed to use this software under the terms of
the GNU General Public License (GPL) versions 3.

You have already accepted the terms of the Open Source license.

QMAKE_MAC_SDK must be set when building on Mac
QMAKE_MAC_SDK must be set when building on Mac
Creating qmake...
Failed to resolve SDK path for 'macosx'
Failed to resolve SDK path for 'macosx'
Failed to resolve SDK path for 'macosx'
Failed to resolve SDK path for 'macosx'
Failed to resolve SDK path for 'macosx'
Failed to resolve SDK path for 'macosx'
Failed to resolve SDK path for 'macosx'
Failed to resolve SDK path for 'macosx'
c -o project.o -fconstant-cfstrings -MMD -g -I/private/tmp/qt5-nwIzhu/qt-everywhere-opensource-src-5.3.2/qtbase/qmake -I/private/tmp/qt5-nwIzhu/qt-everywhere-opensource-src-5.3.2/qtbase/qmake/library -I/private/tmp/qt5-nwIzhu/qt-everywhere-opensource-src-5.3.2/qtbase/qmake/generators -I/private/tmp/qt5-nwIzhu/qt-everywhere-opensource-src-5.3.2/qtbase/qmake/generators/unix -I/private/tmp/qt5-nwIzhu/qt-everywhere-opensource-src-5.3.2/qtbase/qmake/generators/win32 -I/private/tmp/qt5-nwIzhu/qt-everywhere-opensource-src-5.3.2/qtbase/qmake/generators/mac -I/private/tmp/qt5-nwIzhu/qt-everywhere-opensource-src-5.3.2/qtbase/qmake/generators/integrity -I/private/tmp/qt5-nwIzhu/qt-everywhere-opensource-src-5.3.2/qtbase/include -I/private/tmp/qt5-nwIzhu/qt-everywhere-opensource-src-5.3.2/qtbase/include/QtCore -I/private/tmp/qt5-nwIzhu/qt-everywhere-opensource-src-5.3.2/qtbase/include/QtCore/5.3.2 -I/private/tmp/qt5-nwIzhu/qt-everywhere-opensource-src-5.3.2/qtbase/include/QtCore/5.3.2/QtCore -I/private/tmp/qt5-nwIzhu/qt-everywhere-opensource-src-5.3.2/qtbase/src/corelib/global -DHAVE_QCONFIG_CPP -I/private/tmp/qt5-nwIzhu/qt-everywhere-opensource-src-5.3.2/qtbase/mkspecs/macx-clang -I/private/tmp/qt5-nwIzhu/qt-everywhere-opensource-src-5.3.2/qtbase/tools/shared -DQT_BUILD_QMAKE -DQT_BOOTSTRAPPED -DPROEVALUATOR_FULL -DQT_NO_TEXTCODEC -DQT_NO_UNICODETABLES -DQT_NO_COMPONENT -DQT_NO_COMPRESS -DQT_NO_THREAD -DQT_NO_QOBJECT -DQT_NO_GEOM_VARIANT -DQT_NO_DATASTREAM -DQT_CRYPTOGRAPHICHASH_ONLY_SHA1 -DQT_JSON_READONLY /private/tmp/qt5-nwIzhu/qt-everywhere-opensource-src-5.3.2/qtbase/qmake/project.cpp
make: c: No such file or directory

And if you attempt to link into a qt present on the system you encounter:

==> qmake qbs.pro -r
xcode-select: error: tool 'xcodebuild' requires Xcode, but active developer directory '/Library/Developer/CommandLineTools' is a command line tools instance
Project ERROR: Could not resolve Xcode version.

And so on. So there's a hard requirement on having Xcode present on the machine. Even at runtime there's an assumption the machine has Xcode on & available.

Ideally, Qt could reach a situation where the hard requirements on Xcode aren't necessary. It is somewhat of a pain to require users to download the nearly 6GB Xcode package to use the full feature set of Qt.

Downstream Homebrew issue report here: https://github.com/Homebrew/homebrew/issues/32431