Build-Script: FreeBSD Package Preset

[etcwilde]

Adding a preset for building the FreeBSD toolchain and runtime package. This is very similar to the Linux package build, but the main difference is the lack of WASM build. The WASM runtime build system uses GNU extensions in its makefiles that are not compatible with the make or gmake on FreeBSD and therefore cannot be built there.

[etcwilde]

@swift-ci please smoke test

[etcwilde]

preset=freebsd_package
@swift-ci Please test with preset Linux Platform

[etcwilde]

The preset test failure is:

[2025-07-17T23:17:57.960Z] /usr/bin/ld: /tmp/lit-tmp-_jhxz0v8/Library-db3eab.o: relocation R_X86_64_PC32 against protected symbol `$s7Library17UnavailableStructVMa' can not be used when making a shared object
[2025-07-17T23:17:57.960Z] /usr/bin/ld: final link failed: bad value
[2025-07-17T23:17:57.960Z] clang: error: linker command failed with exit code 1 (use -v to see invocation)
[2025-07-17T23:17:57.960Z] <unknown>:0: error: link command failed with exit code 1 (use -v to see invocation)

This is because the bfd linker that the preset is defaulting to on Ubuntu 20.04 is too old to support the relocations that Swift emits. This preset is not intended to run on Linux (though it should work on newer versions of bfd or versions that default /usr/bin/ld to lld), but on FreeBSD, which uses lld as the default linker.