ci: run tests on Mach-O (skip ELF tests), reorder CI jobs

[marxin]

With the integration_tests, the ELF tests are run (linked) even on Mach-O, but there are 2 fundamental problems with the approach:

1. /usr/bin/ld on Mach-O is a system linker that does not support the ELF options:

❯ ld -v
@(#)PROGRAM:ld PROJECT:ld-1230.1
BUILD 06:36:05 Dec  2 2025
configured to support archs: armv6 armv7 armv7s arm64 arm64e arm64_32 i386 x86_64 x86_64h armv6m armv7k armv7m armv7em armv8m.main armv8.1m.main
will use ld-classic for: armv6 armv7 armv7s i386 armv6m armv7k armv7m armv7em
LTO support using: LLVM version 17.0.0 (static support for 29, runtime is 29)
TAPI support using: Apple TAPI version 17.0.0 (tapi-1700.3.8)

2. The system compiler (e.g. gcc) does not produce ELF files:

            cargo run --bin wild -- -flavor gnu -static --gc-sections --wrap=foo --wrap=bar --wrap=baz -o /Users/apple/Programming/wild/wild/tests/build/elf/aarch64/wrap/default/wrap.c.wild /Users/apple/Programming/wild/wild/tests/build/elf/aarch64/wrap/default/wrap.c.o /Users/apple/Programming/wild/wild/tests/build/elf/aarch64/wrap/default/runtime.c.o /Users/apple/Programming/wild/wild/tests/build/elf/aarch64/wrap/default/wrap-1.c.o /Users/apple/Programming/wild/wild/tests/build/elf/aarch64/wrap/default/wrap-2.c.o --validate-output --write-layout --write-trace --dependency-file=/Users/apple/Programming/wild/wild/tests/build/elf/aarch64/wrap/default/wrap.c.wild.deps
        Failed to parse object file `/Users/apple/Programming/wild/wild/tests/build/elf/aarch64/wrap/default/wrap.c.o`
        Unsupported ELF header

That's why I tentatively suggest dropping the cross-platform capability of the integrations tests. Thoughts once that @davidlattimore?

[davidlattimore]

It seems reasonable to not run Linux tests on Mac, but why not continue to run Mac tests on Linux? When doing refactorings (on Linux), it's very useful to be able to at least verify that the Mac code paths in the linker still run OK.

[marxin]

Works for me! Part of the PR is also a reordering of the CI jobs so that we have them grouped by platform (Linux, wasip1, Mach-O, Windows). Hope it makes sense.