Version 0.12.1 of x11-misc/synaptics has been released. The former ebuild + patch doesn't work with the new version, so I've made a new ebuild + patch (attachments below).
Created attachment 21135 [details] synaptics-0.12.1 ebuild
Created attachment 21136 [details, diff] synaptics-0.12.1-makefile-fixup.patch
I actually committed 0.12.1 last night. Take a look at it and let me know if you have any problems with how I did it. Instead of patching, I moved to sed. I also made it respect $CC and $CFLAGS.