install_qt.cmake in qt5-base still uses jom

also we should pass some parallel build argumenet because else building qt takes forever.

Building system jom is very inefficient, try to switch to nmake.

Could you elaborate please?

https://wiki.qt.io/Jom

jom is a clone of nmake to support the execution of multiple independent commands in parallel.

As far as others are aware jom is the tool you use to build Qt.

@heydojo Take it easy, it's just a draft. If using nmake takes longer than jom, I will turn off this PR.

@Neumann-A flag /mp parallel build
nmake can't parallelize, but the compiler [cl.exe] itself is doing a good job

From the issue:

I have one PC (out of 3) where Jom consistently deadlocks (4 Jom process running without any progress for hours) within bigger builds of qt (e.g. qt5-base)

So the issue is not inefficiency (nmake will definitely be less efficient), but it appears there is a correctness issue in Jom on certain machines. Using /MP will be mandatory to have reasonable performance.

why closed?
code that works with the /MP flag

    if(CMAKE_HOST_WIN32)
        #vcpkg_find_acquire_program(JOM)
	find_program(NMAKE nmake)
        set(ENV{CL} /MP)
        set(INVOKE "nmake")
    else()
        find_program(MAKE make)
        set(INVOKE "${MAKE}")
    endif()

@voskrese

1. After testing, the time to use nmake is greater than the time to use jom.
2. According to @ras0219-msft said, we need to solve the jam problem of jom instead of replacing it with nmake.

@JackBoosY.
maybe a solution like the PREFER_NINJA solution in the CMake generator selection?
Let the user set e.g. VCPKG_AVOID_JOM in a triplet to force nmake instead of JOM

@JackBoosY
from JOM the known problem for a long time, at multithreading, it begins to compile the new file, without having compiled dependence, and as a result there is a conflict, dependence is not present, and compilation went, an error

and it can not be fixed, parameters, only changing the code of the JOM