bossa: Fix build with clang ≥ 15

[markmentovai]

Description

Type(s)

• bugfix
• enhancement
• security fix

Tested on

macOS 14.0 23A344 arm64
Xcode 15.0 15A240d

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?
• 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?

@quentinmit

[macportsbot]

Notifying maintainers:
@quentinmit for port bossa.
@stromnov for port py-gnureadline.

[markmentovai]

Upstreaming at shumatech/BOSSA#172, although that repository’s been quiet for over 3 years so it may not get any traction.