how to get Qt 5.4.0 source that works for BOTH Windows and OS X

I need to get Qt 5.4.0 source, make a few changes, then build it on both Windows and Mac OS X (including qtwebkit).

If I download the .zip file, I can build on Windows, but configure won't run on Mac - it doesn't like the line endings, apparently. If I copy configure and qtbase/configure from a .tar.gz Qt5 download, configure gives me a "You don't seem to have 'make' or 'gmake' in your PATH" error.

If I download the .tar.gz file, I can build on Mac, but it's missing configure.bat (and who knows what else), so I can't build on Windows.

If I use git to get the source, I end up with the source of the latest dev branch I think. I need the source of the actual 5.4.0 release. I'm no git expert, so even if I could live with the source on the dev branch, I've never successfully managed to build it.

EDIT: I did manage to get Qt 5.4.0 via git and successfully run perl init-repository. However, when I copy that source to Windows and try to run configure, it is missing qtbase\configure.exe. If I copy configure.exe from the .zip version of Qt 5.4.0, configure fails with C:\qt\qt5_git\qtbase\src\corelib\global\qglobal.h(68) : fatal error C1083: Cannot open include file: 'QtCore/qsystemdetection.h': No such file or directory. Of course, the qsystemdetection.h does exist in the same folder as qglobal.h.

There must be some way to do this! When Qt's whole reason for existence is for cross-platform development, it's just too ironic that Qt5 requires me to maintain 2 separate code bases (one for Windows, one for OS X) just to be able to build it.

So what am I missing? How do I get a copy of Qt 5.4.0 that I can modify slightly, then build on both Windows and OS X?