[clang] [clang-tools-extra] [llvm] [llvm][Support] Add and use errnoAsErrorCode (PR #84423)

[David Blaikie via cfe-commits]

https://github.com/dwblaikie approved this pull request.

Sounds OK to me.

(though several other instances of system_category are touched in this patch - out of curiosity, how are those different from the one fixed case you called out in JSONTransport.cpp? Are the other uses of system_category sort of more benign in some way? Or equally buggy/fixed?

Guess there's no practical test coverage for this? Not worth unit testing JSONTransport to inspect its error code, etc, probably)

https://github.com/llvm/llvm-project/pull/84423