emulators/mame: set PTR64=1 on aarch64

This seems to be required to build on aarch64 as per maintainer.

Reported by: agh@riseup.net (via email)
Approved by: agh@riseup.net (maintainer)
MFH: 2023Q2

(cherry picked from commit d52e96a42a2c9cdec297556a3af047bcfd9e12ee)