fheroes2: use legacysupport.use_mp_libcxx on Mojave and older

[aeiouaeiouaeiouaeiouaeiouaeiou]

Description

icn2img uses std::filesystem since version 1.0.1: ihhub/fheroes2@275ccfd
Failing build: https://build.macports.org/builders/ports-10.9_x86_64-builder/builds/231789/steps/install-port/logs/stdio

Type(s)

• bugfix
• enhancement
• security fix

Tested on

macOS 10.13.6 17G14042 x86_64
Xcode 10.1 10B61

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?

[macportsbot]

Notifying maintainers:
@oleg-derevenetz for port fheroes2.

[oleg-derevenetz]

Hi @aeiouaeiouaeiouaeiouaeiouaeiou @herbygillot thanks! I looked at legacysupport port group at the time, but but in its README there is no mention of std::filesystem support :(

[kencu]

the legacysupport portgroup already takes into account whether you're using libc++, so you don't need to test for clang being the compiler.

[kencu]

like most of macports' portgroups, that change fairly quickly, the documentation for the support for a newer libcxx is in the first paragraphs of the portgroup code (legacysupport-1.1.tcl).

MacPorts support for a newer libc++ has nothing to do with the macports-legacy-support headers or library, which is why it is not documented there.

You could say the support for a newer libc++ should never have been added to the legacysupport PortGroup then, if it doesn't use the macports-legacy-support library and there is some logic to that statement, however it was decided to add it there as the concepts are similar (supporting older systems).

If you are using the newer libc++, then the legacysupport-1.1.tcl PortGroup file will automatically add the proper dependency on macports-libcxx for you, as the code to do that has been added there.