Windows source build does not install qmake or mkspecs

After building Qt 5.9.2 release version from source on Windows with MSVC 2017, doing a "make install" doesn't install the qmake executable or the mkspecs directory. On version 5.9.1, this works correctly. On a debug build of 5.9.2 it works correctly. On Linux, it works correctly.

The steps are:

• untar 5.9.2 source
• cd to source directory
• configure -prefix c:\Qt\5.9.2_msvc2017_release -opensource -confirm-license -release -platform win32-msvc -I c:\pgsql\include -L c:\pgsql\lib -nomake examples -nomake tests -sql-psql -make-tool jom
• jom -j4
• jom install
• observe that c:\Qt\5.9.2_msvc2017\bin does not contain qmake.exe
• observe that c:\Qt\5.9.2_msvc2017\mkspecs does not exist