meson: add workaround for Tiger

[kencu]

and peg meson at 55.3 on Tiger as updates are likely fragile
will update meson occasionally, as we do for libuv on Tiger

Description

Type(s)

• bugfix
• enhancement
• security fix

Tested on

macOS 10.4
Xcode 2.5

Verification

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So -- keeping Tiger alive -- this latest meson fix tries to work around the lack of rpath support in Tiger.

It largely works -- I think better than before, due to some helpful recent changes in meson upstream wherein they seem to be interested in using loader_path themselves for at least some of the in-tree executables.

Appreciate testing by anyone still interested. Perfection is not guaranteed .. (the opposite!) but improvements seem present.

[macportsbot]

Notifying maintainers:
@SoapZA for port meson.

[macportsbot]

Travis Build #14720 Passed.

Lint results

--->  Verifying Portfile for meson
--->  0 errors and 0 warnings found.

Port meson success on xcode10.3. Log
Port meson success on xcode9.4. Log
Port meson success on xcode8.3. Log

[kencu]

The remaining issue I'm finding is when building documentation -- that still errors sometimes, so I've had to disable the documentation building on a couple of gnome ports, eg https://github.com/kencu/TigerPorts/blob/68c148b0a916490825690fe725135f8b130de128/devel/atk/Portfile#L39

[kencu]

Well, I would dearly love to fix the gnome scanner part in meson, but a few hours of poking around did not come up with the magic incantation so far. What does work is to set DYLD_LIBRARY_PATH during destroot to the folder containing the library, so that's what I've been doing lately.

I have one tiny bit to add -- to fix machine detection for "power macintosh" systems, and then I'll push this through.