misc/py-pytorch: fix build with clang >= 19 and libc++ 21

In ports f07b5ade5369 misc/py-pytorch was forced onto llvm:max=15, with
the reason "fix build on 14". Remove this, and add a patch to make it
build with clang >= 19 and libc++ 21.

PR: 292664
Approved by: yuri (maintainer)
MFH: 2026Q1