It's hard to get back into a clean state (e.g. when trying to patch):

/--------
| make[3]: Entering directory '/usr/local/src/debian/qtbase-opensource-src-5.3.2+dfsg/qmake'
| rm -f project.o option.o property.o main.o ioutils.o proitems.o qmakevfs.o qmakeglobals.o qmakeparser.o qmakeevaluator.o qmakebuiltins.o makefile.o unixmake2.o unixmake.o mingw_make.o winmakefile.o projectgenerator.o meta.o makefiledeps.o metamakefile.o xmloutput.o pbuilder_pbx.o msvc_vcproj.o msvc_vcxproj.o msvc_nmake.o msvc_objectmodel.o msbuild_objectmodel.o gbuild.o cesdkhandler.o qtextcodec.o qutfcodec.o qstring.o qstring_compat.o qstringbuilder.o qtextstream.o qiodevice.o qmalloc.o qglobal.o qarraydata.o qbytearray.o qbytearraymatcher.o qdatastream.o qbuffer.o qlist.o qfiledevice.o qfile.o qfilesystementry.o qfilesystemengine.o qfsfileengine.o qfsfileengine_iterator.o qregexp.o qvector.o qbitarray.o qdir.o qdiriterator.o quuid.o qhash.o qfileinfo.o qdatetime.o qstringlist.o qabstractfileengine.o qtemporaryfile.o qmap.o qmetatype.o qsettings.o qsystemerror.o qlibraryinfo.o qvariant.o qvsnprintf.o qlocale.o qlocale_tools.o qlinkedlist.o qnumeric.o qcryptographichash.o qxmlstream.o qxmlutils.o qlogging.o qjson.o qjsondocument.o qjsonparser.o qjsonarray.o qjsonobject.o qjsonvalue.o qfilesystemengine_unix.o qfilesystemiterator_unix.o qfsfileengine_unix.o qlocale_unix.o
| rm -rf .deps
| rm -f /usr/local/src/debian/qtbase-opensource-src-5.3.2+dfsg/bin/qmake
| make[3]: Leaving directory '/usr/local/src/debian/qtbase-opensource-src-5.3.2+dfsg/qmake'
| cd src/ && ( test -e Makefile || /usr/local/src/debian/qtbase-opensource-src-5.3.2+dfsg/bin/qmake /usr/local/src/debian/qtbase-opensource-src-5.3.2+dfsg/src/src.pro -o Makefile ) && /usr/bin/make -f Makefile distclean
| make[3]: Entering directory '/usr/local/src/debian/qtbase-opensource-src-5.3.2+dfsg/src'
| /usr/local/src/debian/qtbase-opensource-src-5.3.2+dfsg/bin/qmake -o Makefile src.pro
| make[3]: /usr/local/src/debian/qtbase-opensource-src-5.3.2+dfsg/bin/qmake: Command not found
| Makefile:757: recipe for target 'Makefile' failed
| make[3]: *** [Makefile] Error 127
| make[3]: Leaving directory '/usr/local/src/debian/qtbase-opensource-src-5.3.2+dfsg/src'
| Makefile:50: recipe for target 'sub-src-distclean' failed
| make[2]: *** [sub-src-distclean] Error 2
| make[2]: Leaving directory '/usr/local/src/debian/qtbase-opensource-src-5.3.2+dfsg'
| debian/rules:142: recipe for target 'override_dh_auto_clean' failed
| make[1]: *** [override_dh_auto_clean] Error 2
| make[1]: Leaving directory '/usr/local/src/debian/qtbase-opensource-src-5.3.2+dfsg'
| debian/rules:92: recipe for target 'clean' failed
| make: *** [clean] Error 2
\--------

It appears we remove the 'qmake' binary but then still want to use it to
make the rules to clean the rest of the build tree.