fix(runtime-c-api) Set the install name of the dylib to @rpath.

```sh
$ objdump -macho -dylib-id libwasmer_runtime_c_api.dylib
libwasmer_runtime_c_api.dylib:
/Users/distiller/project/target/release/deps/libwasmer_runtime_c_api.dylib
```

we observe that the dylib ID (aka install name) is set to
`/Users/distiller/project/target/release/deps/libwasmer_runtime_c_api.dylib`,
which is valid only in the context of CircleCI.

This patch changes the dylib ID to
`@rpath/libwasmer_runtime_c_api.dylib`, which can be then changed by
the linker option `-rpath` (use `-Wl,-rpath,$value` with the compiler
to send the `-rpath` value to the linker).

This is super useful when dynamically linking libraries against
another language.

.circleci/config.yml

@@ -284,10 +284,11 @@ jobs:
             # VERSION=$(cargo pkgid | cut -d# -f2 | cut -d: -f2)
             # echo "${VERSION}" >> artifacts/version
       - run:
-          name: Dynamic library
+          name: Generate dynamic library for the runtime C API
           command: |
             export PATH="$HOME/.cargo/bin:$PATH"
             cargo build --release --manifest-path lib/runtime-c-api/Cargo.toml
+            install_name_tool -id "@rpath/libwasmer_runtime_c_api.dylib" target/release/libwasmer_runtime_c_api.dylib
             cp target/release/libwasmer_runtime_c_api.dylib ./artifacts
       - persist_to_workspace:
           root: .