Sometimes INSTALL_ROOT is undefined in Makefile

make[3]: Leaving directory '/home/scratch/sources/qt5/qt-57-build-android/qttools/src/qdoc'
cd qtplugininfo/ && ( test -e Makefile || /home/scratch/sources/qt5/qt-57-build-android/qtbase/bin/qmake /home/scratch/sources/qt5/qt5-git/qttools/src/qtplugininfo/qtplugininfo.pro -qtconf /home/scratch/sources/qt5/qt-57-build-android/qtbase/bin/qt.conf -o Makefile ) && make -f Makefile install

make[3]: Entering directory '/home/scratch/sources/qt5/qt-57-build-android/qttools/src/qtplugininfo'

mkdir: cannot create directory ‘/libs’: Permission denied

Makefile:1025: recipe for target 'install_target' failed
make[3]: *** [install_target] Error 1
make[3]: Leaving directory '/home/scratch/sources/qt5/qt-57-build-android/qttools/src/qtplugininfo'
Makefile:211: recipe for target 'sub-qtplugininfo-install_subtargets' failed
make[2]: *** [sub-qtplugininfo-install_subtargets] Error 2
make[2]: Leaving directory '/home/scratch/sources/qt5/qt-57-build-android/qttools/src'
Makefile:56: recipe for target 'sub-src-install_subtargets' failed
make[1]: *** [sub-src-install_subtargets] Error 2
make[1]: Leaving directory '/home/scratch/sources/qt5/qt-57-build-android/qttools'
Makefile:841: recipe for target 'module-qttools-install_subtargets' failed
make: *** [module-qttools-install_subtargets] Error 2

install_target: first FORCE
        @test -d $(INSTALL_ROOT)/libs/armeabi-v7a/ || mkdir -p $(INSTALL_ROOT)/libs/armeabi-v7a/
        -$(INSTALL_PROGRAM) ../../bin/$(QMAKE_TARGET) $(INSTALL_ROOT)/libs/armeabi-v7a/$(QMAKE_TARGET)