py-greenlet: fix build for powerpc

[barracuda156]

Description

Fix this finally

Type(s)

• bugfix
• enhancement
• security fix

Tested on

macOS 10.6
Xcode 3.2

Verification

Have you

• followed our Commit Message Guidelines?
• squashed and minimized your commits?
• checked that there aren't other open pull requests for the same change?
• referenced existing tickets on Trac with full URL in commit message?
• checked your Portfile with port lint --nitpick?
• tried existing tests with sudo port test?
• tried a full install with sudo port -vst install?
• tested basic functionality of all binary files?
• checked that the Portfile's most important variants haven't been broken?

[macportsbot]

Notifying maintainers:
@stromnov for port py-greenlet.

[barracuda156]

Failure on macOS 14 CI is unrelated: it is Python 3.5–3.6 failing to build.

[barracuda156]

@stromnov @reneeotten Could we merge this one?

[berg-michael]

I observe the same issue when building on 10.4 PPC. AFAICT almost all of the changes here are behind PPC only headers (read: shouldn't be any collateral damage to other targets).