[CentOS-devel] Is which requried for rpm-build?

I've been using centos dockers for a while to build images.

With the latest Centos update 7.2.1511 to the docker images, I am no longer
able to build rpm packages without manually installing which.

I get an error similar to this

    rpmbuild -ba /home/dev/rpmbuild/SPECS/re2c.spec
    sh: which: command not found
    sh: which: command not found
    Executing(%prep):  -e /var/tmp/rpm-tmp.9WC5EP
    error: Exec of /var/tmp/rpm-tmp.9WC5EP failed (%prep): No such file or
directory
    error: Bad exit status from /var/tmp/rpm-tmp.9WC5EP (%prep)


    RPM build errors:
        Bad exit status from /var/tmp/rpm-tmp.9WC5EP (%prep)

No matter how simple my spec is...

I can run "sh /var/tmp/rpm-tmp.9WC5EP" without issue. So I'm still not 100%
sure where the problem REALLY lies.

The only packages I've installed is

    yum groupinstall "Development Tools"

My question is where is the error, and where can I file/view a bug report?
Should rpm-build from https://git.centos.org/summary/?r=rpms/rpm have
"Requires: which" for the build package? Or is which supposed to be in
"Development tools", or am I just doing this all wrong?

Thanks
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