Change default directory used by USES=autoreconf to WRKSRC

[jbeich]

Test Plan

USES=autoreconf ports that change CONFIGURE_WRKSRC:

• graphics/p5-ming
• graphics/py-ming

[jbeich]

• Fix graphics/p[5y]-ming by not poking USE_GITHUB variables instead of redefining AUTORECONF_WRKSRC

[jbeich]

Oops, use PATCH_WRKSRC in post-patch to avoid confusion.

[tijl]

For me the patch is fine, but I would just use ${WRKSRC}/perl_ext (or py_ext) in post-patch. Since autoreconf runs in WRKSRC it's possible that in the future some files may need to be patched there and then a non-default PATCH_WRKSRC can be a bit confusing or unexpected.

[jbeich]

In D4169#87753, @tijl wrote:

I would just use ${WRKSRC}/perl_ext (or py_ext) in post-patch.

graphics/py-ming already relies on non-default PATCH_WRKSRC as it modifies WRKSRC. I've tried to keep p5-ming consistent with it. However, rebasing the patches would complicate this differential even more.

Let's go back to AUTORECONF_WRKSRC then. Improving p[5y]-ming ports is out of scope here.

[jbeich]

Rebased.