QtWebEngine apparently gets skipped during build

I've downloaded the 5.12.3 sources for windows but it looks like building webengine is silently skipped.

I'm attempting to build on Windows 10 64bit, from a VS2017 native x64 command prompt.

Following version of required tools are installed:

• Python 2.7.16
• Byson 3.0
• flex 2.5.37
• gperf 3.0.1

I'm performing an out of source build with the source files in C:\qt5-12.3 and have set the build folder to C:\Qt-5.12.3-Build.

Configure options:

configure.bat -top-level -opensource -debug-and-release -opengl desktop -nomake examples -nomake tests -confirm-license -skip qtdoc -qtnamespace Qt_5_12_3 -prefix \Qt-5.12.3-Build\qtbase

when building using

nmake && echo "BUILD SUCCESS"

"BUILD SUCCESS" is output, but the build time is way too short for webengine to have been built (after a subsequent "nmake install" the webengine dll still is nowhere to be found).

Any idea what is going wrong here? If the webengine build is being skipped because something is missing or wrong, I expect to get at least an error to notify about it.