When building the Qt 5.6.0 beta snapshot from the source file qt-everywhere-opensource-src-5.6.0-beta.tar.gz dated 03-Nov-2015 09:29, the build stops with this error:

cd qtdoc/ && ( test -e Makefile || /home/tranter/ics/qt-everywhere-opensource-src-5.6.0-beta/qtbase/bin/qmake /home/tranter/ics/qt-everywhere-opensource-src-5.6.0-beta/qtdoc/qtdoc.pro -o Makefile ) && make -f Makefile
make[1]: Entering directory `/home/tranter/ics/qt-everywhere-opensource-src-5.6.0-beta/qtdoc'
cd doc/ && ( test -e Makefile || /home/tranter/ics/qt-everywhere-opensource-src-5.6.0-beta/qtbase/bin/qmake /home/tranter/ics/qt-everywhere-opensource-src-5.6.0-beta/qtdoc/doc/doc.pro -o Makefile ) && make -f Makefile
Cannot find file: /home/tranter/ics/qt-everywhere-opensource-src-5.6.0-beta/qtdoc/doc/doc.pro.
make[1]: *** [sub-doc-make_first] Error 2
make[1]: Leaving directory `/home/tranter/ics/qt-everywhere-opensource-src-5.6.0-beta/qtdoc'
make: *** [module-qtdoc-make_first] Error 2

The qtdoc/doc/ directory is empty (it is missing from the source archive).
Previous Qt releases and Qt 5.6.0 alpha contained files in this directory.
It seems to have been left out of the source snapshot.