You don't unless you have the 10.6 SDK installed and it somehow works with your version of Xcode.

My 2 cents: Honestly, I wouldn't worry about it. Make your builds for i386 and x86_64 and someone with an old machine who has the interest to build and upload it can help you out. 10.6 came out 10 years ago and was the last version to support ppc so it's nice to support it, in theory, in practice it's probably not worth your time unless you have extra and an old machine + build tools ready to go.

On Jun 12, 2019, at 6:07 PM, pd-list-request@lists.iem.at wrote:

Date: Wed, 12 Jun 2019 13:07:11 -0300
From: Alexandre Torres Porres <porres@gmail.com>
To: Pd-List <pd-list@lists.iem.at>
Subject: [PD] hints on how to compile for mac PPC on an intel
Message-ID:
<CAEAsFmieRVRMNME5J6CDKoSHxitibm6=i+fjLUhJ=QkpeMM4=Q@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"

Hi, I thought I had taken care of every platform when compiling my
externals, but there's still PPC to go :)

Any hints on how to compile for mac PPC on an intel mac?

--------
Dan Wilcox
@danomatika
danomatika.com
robotcowboy.com