Make Wasm link section conditional on compiler version

[dtolnay]

In order to avoid triggering a link error where there didn't used to be one. #74 causes rust-lld errors like this in compilers older than nightly-2024-12-19:

error: linking with `wasm-component-ld` failed: exit status: 1
  |
  = note: "wasm-component-ld" "-flavor" "wasm" "--export" "__main_void" "--export" "cabi_realloc" "-z" "stack-size=1048576" "--stack-first" "--allow-undefined" "--no-demangle" {...} "-l" "c" "-L" ".rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/wasm32-wasip2/lib/self-contained" "-o" "target/wasm32-wasip2/debug/deps/repro-2c59c9d65bdd9014.wasm" "--gc-sections" "-O0"
  = note: rust-lld: error: target/wasm32-wasip2/debug/deps/repro-2c59c9d65bdd9014.am9l6ff8xuqu3stbvow8o8tiz.rcgu.o: invalid data symbol offset: `_ZN5repro1_6__CTOR17h2780dd13c1356084E` (offset: 4 segment size: 1)
          error: failed to invoke LLD: exit status: 1