[stdlib] Both FreeBSD and OpenBSD use environ.

However, when building Glibc with assertions enabled, LLVM asserts in
CodeGenModule::EmitGlobal with "Cannot emit local var decl as global".
This assert is _probably_ wrong in LLVM because the local extern
reference isn't being handled properly and needs to be addressed there.
We could move the declaration to global scope, but that is not ideal
because it makes the pointer declaration visible to Swift.

OpenBSD needs to implement _swift_stdlib_getEnviron regardless, so
let's do so.

Author: 3405691582

stdlib/public/SwiftShims/LibcOverlayShims.h

@@ -52,7 +52,7 @@ static inline int _swift_stdlib_fcntlPtr(int fd, int cmd, void* ptr) {
 #endif
 
 // Environment
-#if defined(__FreeBSD__)
+#if defined(__FreeBSD__) || defined(__OpenBSD__)
 static inline char * _Nullable * _Null_unspecified _swift_stdlib_getEnviron() {
   extern char **environ;
   return environ;