configure on Windows can't handle unquoted -DFOO=0 arguments

It appears that the configure.bat script on windows can't properly handle -DFOO=<single-digit> assignments

See the following outputs:

..\qtbase\configure -- -DFOO=0
-- -DFOO= # this gets echoed for no reason
'E:/dev/cmakes/cmake-3.28.3/bin/cmake.exe' '-DQT_INTERNAL_CALLED_FROM_CONFIGURE:BOOL=TRUE' '-G' 'Ninja' 'E:/dev/qt/src/qt6_alt/qtbase' # no -DFOO argument at all

..\qtbase\configure -- -DFOO=1
'E:/dev/cmakes/cmake-3.28.3/bin/cmake.exe' '-DFOO=' '-DQT_INTERNAL_CALLED_FROM_CONFIGURE:BOOL=TRUE' '-G' 'Ninja' 'E:/dev/qt/src/qt6_alt/qtbase'
# -DFOO= is missing its value

# Same as -DFOO=0, it gets echoed, and no -DFOO argument at all
..\qtbase\configure -- -DFOO=2
-- -DFOO=
'E:/dev/cmakes/cmake-3.28.3/bin/cmake.exe' '-DQT_INTERNAL_CALLED_FROM_CONFIGURE:BOOL=TRUE' '-G' 'Ninja' 'E:/dev/qt/src/qt6_alt/qtbase'

Same happens for -DFOO=3 up to -DFOO=9.
-DFOO=10 works fine.

It works fine for -DFOO=ON / -DFOO=OFF or -DFOO=<some_non_digit_value>.

This happens starting with Qt 6.2, when we switched to passing the bat arguments to configure by first writing them into a file: https://codereview.qt-project.org/c/qt/qtbase/+/366271

Specifically

echo %*>config.opt.in

My guess is that the echo command treats the equal sign in -DFOO=1 as a delimiter, but only sometimes. But it doesn't explain why some other equal assignments work fine, so this theory might be wrong.

In Qt 5 we didn't have this problem presumably because we use the following construct:

set ARGS=%*
...
"%QTDIR%\bin\qmake.exe" "%TOPQTSRC%" -- %ARGS%

ss64 says

If you use %* to refer to all parameters, the value returned will include the delimiters.

So I guess assigning '%*' to a variable ARGS and expanding %ARGS% to a command invocation, instead of echo-ing preserves the values.

At least
https://ss64.com/nt/syntax-esc.html
and
https://stackoverflow.com/questions/20572424/preserving-equal-characters-in-batch-file-parameters
claim that it's not really possible to preserve the exact arguments that contain '=' when echoing, unless they are quoted, but again, i might be wrong. At least i haven't found a solution yet.

Finally, the correct quoting necessary is different when calling configure.bat in cmd.exe vs powershell.

In cmd.exe you need to use

..\qtbase\configure -- "-DFOO=2"

in powershell you need to use

..\qtbase\configure -- '"-DFOO=2"'

the single quotes are for powershell to keep the literal double quotes, so they get passed along to the bat processor.