[llvm][Support] Add and use errnoAsErrorCode (#84423)

LLVM is inconsistent about how it converts `errno` to `std::error_code`.
This can cause problems because values outside of `std::errc` compare
differently if one is system and one is generic on POSIX systems.

This is even more of a problem on Windows where use of the system
category is just wrong, as that is for Windows errors, which have a
completely different mapping than POSIX/generic errors. This patch fixes
one instance of this mistake in `JSONTransport.cpp`.

This patch adds `errnoAsErrorCode()` which makes it so people do not
need to think about this issue in the future. It also cleans up a lot of
usage of `errno` in LLVM and Clang.

1 files changed, 1 insertions, 1 deletions

diff --git a/llvm/lib/Support/LockFileManager.cpp b/llvm/lib/Support/LockFileManager.cpp
index facdc5a..083f8d7 100644
--- a/llvm/lib/Support/LockFileManager.cpp
+++ b/llvm/lib/Support/LockFileManager.cpp
@@ -87,7 +87,7 @@ static std::error_code getHostID(SmallVectorImpl<char> &HostID) {
   struct timespec wait = {1, 0}; // 1 second.
   uuid_t uuid;
   if (gethostuuid(uuid, &wait) != 0)
-    return std::error_code(errno, std::system_category());
+    return errnoAsErrorCode();
 
   uuid_string_t UUIDStr;
   uuid_unparse(uuid, UUIDStr);