Gprbuild -cflags

Can somebody tell me what is wrong with the following (extracted from running alr -v on an arm64 Mac):

gprbuild -s -j0 -p -P /Users/pmunts/src/libsimpleio/ada/programs/alire/test_remoteio_led/test_remoteio_led.gpr -cflags -mmacosx-version-min=26.0
gprbuild: illegal option "-cflags" on the command line

I cannot see how -cargs violates the gprbuild command line syntax (though -s -j0 -p seems to violate a strict reading):

gprbuild --help

Usage: gprbuild [-P<proj>] [<proj>.gpr] [opts] [name]

    {[-cargs opts] [-cargs:lang opts] [-largs opts] [-kargs opts] [-gargs opts]}
"-cflags" /= "-cargs"