Fix search of jom to ensure it works with execute_process

Since CMake execute_process, let's teach find_program to explicitly
look for the ".bat" and then the ".exe".

Indeed, after installing jom using chocolatey, the two files
available in the path are:
 - C:\Chocolatey\bin\jom
 - C:\Chocolatey\bin\jom.bat
These two file are both "bat" file and by default "find_program" will find
the one without extension and consider it is a regular exectuable. By
explicitly finding the ".bat" file, execute_process will know how to deal
with it based on its extension.
Re-attempt Qt configure or build step only if required