"The encapsulation symbol needs to be retained under --gc-sections properly"

The current master branch fails to build on FreeBSD 14.0-CURRENT amd64, even though it still works on FreeBSD stable/13.
```
$ cargo test
...
= note: ld: error: undefined symbol: __start_linkme_SHENANIGANS
>>> referenced by x4z07wsgcl2z4i4
>>> /usr/home/somers/src/rust/linkme/target/debug/deps/distributed_slice-425b465e5440679a.x4z07wsgcl2z4i4.rcgu.o:(distributed_slice::SHENANIGANS::hca25c6519cd4df0f)
>>> the encapsulation symbol needs to be retained under --gc-sections properly; consider -z nostart-stop-gc (see https://lld.llvm.org/ELF/start-stop-gc)

ld: error: undefined symbol: __stop_linkme_SHENANIGANS
>>> referenced by x4z07wsgcl2z4i4
>>> /usr/home/somers/src/rust/linkme/target/debug/deps/distributed_slice-425b465e5440679a.x4z07wsgcl2z4i4.rcgu.o:(distributed_slice::SHENANIGANS::hca25c6519cd4df0f)

ld: error: undefined symbol: __start_linkme_EMPTY
>>> referenced by x4z07wsgcl2z4i4
>>> /usr/home/somers/src/rust/linkme/target/debug/deps/distributed_slice-425b465e5440679a.x4z07wsgcl2z4i4.rcgu.o:(distributed_slice::test_empty::EMPTY::h31c7f9e37773eb8f)
>>> the encapsulation symbol needs to be retained under --gc-sections properly; consider -z nostart-stop-gc (see https://lld.llvm.org/ELF/start-stop-gc)

ld: error: undefined symbol: __stop_linkme_EMPTY
>>> referenced by x4z07wsgcl2z4i4
>>> /usr/home/somers/src/rust/linkme/target/debug/deps/distributed_slice-425b465e5440679a.x4z07wsgcl2z4i4.rcgu.o:(distributed_slice::test_empty::EMPTY::h31c7f9e37773eb8f)

ld: error: undefined symbol: __start_linkme_NONCOPY
>>> referenced by x4z07wsgcl2z4i4
>>> /usr/home/somers/src/rust/linkme/target/debug/deps/distributed_slice-425b465e5440679a.x4z07wsgcl2z4i4.rcgu.o:(distributed_slice::test_non_copy::NONCOPY::h920eb5b4a050a94d)
>>> the encapsulation symbol needs to be retained under --gc-sections properly; consider -z nostart-stop-gc (see https://lld.llvm.org/ELF/start-stop-gc)

ld: error: undefined symbol: __stop_linkme_NONCOPY
>>> referenced by x4z07wsgcl2z4i4
>>> /usr/home/somers/src/rust/linkme/target/debug/deps/distributed_slice-425b465e5440679a.x4z07wsgcl2z4i4.rcgu.o:(distributed_slice::test_non_copy::NONCOPY::h920eb5b4a050a94d)
cc: error: linker command failed with exit code 1 (use -v to see invocation)

error: could not compile `linkme` due to previous error
error: could not compile `linkme` due to previous error
error: could not compile `linkme` due to previous error
```