`runtime/environment.cpp` doesn't compile on FreeBSD:
```
runtime/environment.cpp:115:47: error: use of undeclared identifier 'RTLD_DEFAULT'
115 | auto envpp{reinterpret_cast<char ***>(dlsym(RTLD_DEFAULT, "environ"))};
| ^~~~~~~~~~~~
```
`<dlfcn.h>` needs to be included.
Tested on `x86_64-pc-freebsd15.1` and `x86_64-pc-linux-gnu`.
(cherry picked from commit 20102748a3548a1006e32056868cb3df8ce83565)