Fix macOS N-API linking by allowing undefined symbols

Add -undefined dynamic_lookup linker flags for macOS targets to allow
N-API symbols to be resolved at runtime by Node.js instead of failing
at build time.

Author: penberg

.cargo/config.toml

@@ -1,3 +1,9 @@
+[target.x86_64-apple-darwin]
+rustflags = ["-C", "link-arg=-undefined", "-C", "link-arg=dynamic_lookup"]
+
+[target.aarch64-apple-darwin]
+rustflags = ["-C", "link-arg=-undefined", "-C", "link-arg=dynamic_lookup"]
+
 [target.aarch64-unknown-linux-musl]
 linker = "aarch64-alpine-linux-musl-gcc"
 rustflags = ["-C", "target-feature=-crt-static"]