qmake system() does not work under qemu-user

The qmake system() call to run programs does not work when running under qemu-user emulation (aarch64 guest under x86-64 host). This is because it probably uses posix_spawn() or some other API to launch processes that in turn calls clone() and clone() is not fully supported under qemu-user emulation. Relevant issue in the qemu project: https://gitlab.com/qemu-project/qemu/-/issues/140

strace log extract of running

echo | qmake /dev/stdin

1576461 clone(0x1011,child_stack=0x0000000000000000,parent_tidptr=0x0000005501990f70,tls=0x0000000000000000,child_tidptr=0x0000000000000000) = -1 errno=22 (Invalid argument)

we see clone fails.

It would be nice if qmake could use fork+exec or similar to run processes instead of posix_spawn(). This bug makes it impossible to build projects (such as PyQt) that use qmake under qemu-user which is much more convenient than running a full VM.

work-around

configure with -no-feature-forkfd_pidfd