Linker warnings on macOS: no platform load command found in ... assuming: macOS

[JoergAtGithub]

Maybe an Xcode issue: ispc/ispc#2678

Originally posted by @daschuer in #15686 (comment)

2.6 builds on macOS shows:

[954/959] Linking CXX executable Mixxx.app/Contents/MacOS/Mixxx
ld: warning: no platform load command found in '/Users/runner/buildenv/mixxx-deps-2.6-x64-osx-rel-da4c207/installed/x64-osx-min1100-release/lib/libavcodec.a[x86_64]762', assuming: macOS
ld: warning: no platform load command found in '/Users/runner/buildenv/mixxx-deps-2.6-x64-osx-rel-da4c207/installed/x64-osx-min1100-release/lib/libavcodec.a[x86_64]764', assuming: macOS
ld: warning: no platform load command found in '/Users/runner/buildenv/mixxx-deps-2.6-x64-osx-rel-da4c207/installed/x64-osx-min1100-release/lib/libavcodec.a[x86_64]766', assuming: macOS
ld: warning: no platform load command found in '/Users/runner/buildenv/mixxx-deps-2.6-x64-osx-rel-da4c207/installed/x64-osx-min1100-release/lib/libavcodec.a[x86_64]768', assuming: macOS
ld: warning: no platform load command found in '/Users/runner/buildenv/mixxx-deps-2.6-x64-osx-rel-da4c207/installed/x64-osx-min1100-release/lib/libavcodec.a[x86_64]770', assuming: macOS
ld: warning: no platform load command found in '/Users/runner/buildenv/mixxx-deps-2.6-x64-osx-rel-da4c207/installed/x64-osx-min1100-release/lib/libavcodec.a[x86_64]773', assuming: macOS
...