[OE-core] [PATCH 1/1] rpm_4.14.0: clamp timestamps by default

[Bystricky, Juro]

> I'm not sure I understand the necessity of this. What matters for
> reproducibility is that rpms install the same files; why is it important
> that the rpm file itself has exactly same build time and is otherwise
> identical bit by bit?
> 

There is actually a demand for binary reproducible packages.
See for example https://wiki.debian.org/ReproducibleBuilds/About
Debian packages already clamp timestamps by default. I am not even sure you can disable this 
(short of unsetting SOURCE_CODE_EPOCH). The same functionality exists for RPM packages,
except it is not the default behavior.

> A technicality: do not patch mnacros.in, set the macro directly from
> package_rpm.bbclass.
>

Yes, I considered this (see the [patch 0/1]). I chose to patch macros.in in the 
recipe rpm_4.14.0 instead because the new macro is introduced in RPM 4.14.0. 
I assumed we did not want to have RPM version dependencies in package_rpm.bbclass. 
But I have no strong feelings regarding this, I am pretty sure the new macro is here
to stay in the future and it is unlikely anyone would want to use a pre-4.14.0 
version of RPM either. If you think patching package_rpm.bbclass makes more sense,
I can send in another patch.
 
Juro