Use Debian 8 (Jessie) as the template to create a new container. You can build the source directly inside Proxmox, but I didn’t want to dirty my Proxmox install with a bunch of development libraries, so instead I created a new Debian container in Proxmox for building. I’ve applied the patch to my copy of Proxmox 4.4’s version of QEMU, which is currently pve-qemu-kvm 2.7.1-4. deb package, skip to the next section, otherwise you can follow these build instructions to create it yourself. If you just want to download the fixed QEMU. Instead, we can patch QEMU to fix the SMC support, using the fixes from here:

One way of fixing this would be to remove the SMC device from the virtual machine’s arguments, and use FakeSMC.kext instead, like a regular Hackintosh, but this is inelegant. Proxmox 5.1 now includes the fix for this problem in its regular QEMU package so a patch for 5.1 is no longer necessary. This causes a fatal error during boot on Proxmox 4 and earlier.

In Sierra 10.12.4, macOS added some extra copy protection which is able to tell that the SMC emulation that QEMU provides is not a real Mac.

Boot disc for mac os sierra 10.12.4