Starting from a fresh source tree (git master branch) on OS X Lion with latest Xcode:

$ cd /path/to/qt
$ ./configure -prefix $PWD/qtbase -opensource -developer-build
$ make
(all steps past this should ideally not be required at all, but that's a different bug!)
$ cd qtjsbackend
$ make
$ find ../qtbase/lib/QtV8.framework/
../qtbase/lib/QtV8.framework/
../qtbase/lib/QtV8.framework//Contents
../qtbase/lib/QtV8.framework//Contents/Info.plist
../qtbase/lib/QtV8.framework//QtV8_debug
../qtbase/lib/QtV8.framework//QtV8_debug.prl
../qtbase/lib/QtV8.framework//Versions
../qtbase/lib/QtV8.framework//Versions/5
../qtbase/lib/QtV8.framework//Versions/5/QtV8_debug
../qtbase/lib/QtV8.framework//Versions/Current

that's incomplete: it should rather look more like this

../qtbase/lib/QtV8.framework
../qtbase/lib/QtV8.framework/Contents
../qtbase/lib/QtV8.framework/Contents/Info.plist
../qtbase/lib/QtV8.framework/Headers
../qtbase/lib/QtV8.framework/QtV8
../qtbase/lib/QtV8.framework/QtV8.prl
../qtbase/lib/QtV8.framework/QtV8_debug
../qtbase/lib/QtV8.framework/QtV8_debug.prl
../qtbase/lib/QtV8.framework/Versions
../qtbase/lib/QtV8.framework/Versions/5
../qtbase/lib/QtV8.framework/Versions/5/Headers
../qtbase/lib/QtV8.framework/Versions/5/Headers/QtV8
../qtbase/lib/QtV8.framework/Versions/5/QtV8
../qtbase/lib/QtV8.framework/Versions/5/QtV8_debug
../qtbase/lib/QtV8.framework/Versions/Current

So, if we press on:

$ cd ../qtdeclarative
$ make

eventually we get

ld: framework not found QtV8

If we had run configure with the -release option, it works fine, but then it's not possible to build some of the autotests, which is why I wanted to create a developer build. It also works if I do both builds and then supply the missing files from the release version of the QtV8 framework into the developer version:

$ cd /path/to/qt-dev-version/qtbase
$ rsync -avu /path/to/qt-release-version/qtbase/lib/QtV8.framework lib/
$ cd ../qtdeclarative
$ make