If Python 2.7.10 or later is installed on system, configure can't find that.
Showing running configure:
WARNING: Python version 2 (2.7.5 or later) is required to build QtWebEngine.
Showing to start building WebEngine:
cd qtwebengine/ && ( test -e Makefile || /Users/akihitoi/Qt/5.13.0/Src/build/qtbase/bin/qmake -o Makefile /Users/akihitoi/Qt/5.13.0/Src/qtwebengine/qtwebengine.pro ) && /Applications/Xcode.app/Contents/Developer/usr/bin/make -f Makefile
A suitable version of python2 could not be found.
QtWebEngine will not be built.
Python 2.7.10 is default on macOS 10.14 Mojave, that have to be downgraded to 2.7.9. If latest 2.7.16 is installed, won't work.