The reason it fails is due to this change in the spec file:

-make %{?_smp_mflags} +%make_build

Because this substitution was performed by spec-cleaner, I consider this a bug on the SLE_12_SP4 platform because its build environment lacks a definition of the %make_build macro. I considered filing a bug report - but then again, if recent versions of the spec-cleaner are also used by SLE developers, they must be aware of it already, so it probably will get fixed (by SUSE) sooner or later, anyway.

So, yeah, we don't care.