[llvm] [flang][runtime] Use dlsym to access char** environ on FreeBSD (PR #158477)

[Michael Kruse via llvm-commits]

Meinersbur wrote:

We reviewers usually assume that the author will land the PR themselves after it is approved. If you do not have permission to do that, would you like me to land this PR?

https://github.com/llvm/llvm-project/pull/158477