[llvm] [Support] Only enable use of /proc/self/fd on Linux (PR #222497)

[via llvm-commits]

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@@ -1027,11 +1027,7 @@ ErrorOr<basic_file_status> directory_entry::status() const {
   return s;
 }
 
-//
-// FreeBSD optionally provides /proc/self/fd, but it is incompatible with
-// Linux. The thing to use is realpath.
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zhangweize9-cyber wrote:

Please pay attention to the comment here.

https://github.com/llvm/llvm-project/pull/222497