Use a long-established error code instead of a newfangled one which causes portability problems

[he32]

Summary

Use the long-established operation_not_supported instead of the rather newfangled state_not_recoverable error code.
The latter is not available on NetBSD 9.x, due to the host system not having ENOTRECOVERABLE
defined. NetBSD-current has it and the coming 10.0 will have it, though.

However, it can also be argued that operation_not_supported is a better fit for the actual error message,
which in essence says "Incremental mode for action %d is not supported".

clang/lib/Interpreter/IncrementalParser.cpp

           switch (CI.getFrontendOpts().ProgramAction) {
           default:
             Err = llvm::createStringError(
-                std::errc::state_not_recoverable,
+                std::errc::operation_not_supported,
                 "Driver initialization failed. "
                 "Incremental mode for action %d is not supported",
                 CI.getFrontendOpts().ProgramAction);