handle EROFS in create/open file

I hit an unexpected errno 30 on macos attempting to call createFile on a
directory in PATH.  errno 30 is EROFS, this change propagates that error
as error.ReadOnlyFileSystem.

lib/std/Io/Dispatch.zig

@@ -2512,6 +2512,7 @@ fn dirCreateFile(
             .OPNOTSUPP => return error.FileLocksUnsupported,
             .AGAIN => return error.WouldBlock,
             .TXTBSY => return error.FileBusy,
+            .ROFS => return error.ReadOnlyFileSystem,
             .NXIO => return error.NoDevice,
             .ILSEQ => return error.BadPathName,
             else => |err| return unexpectedErrno(err),
@@ -2647,6 +2648,7 @@ fn dirOpenFile(
             .AGAIN => return error.WouldBlock,
             .TXTBSY => return error.FileBusy,
             .NXIO => return error.NoDevice,
+            .ROFS => return error.ReadOnlyFileSystem,
             .ILSEQ => return error.BadPathName,
             else => |err| return unexpectedErrno(err),
         }

lib/std/Io/File.zig

@@ -202,6 +202,7 @@ pub const OpenError = error{
     NotDir,
     /// The path already exists and the `CREAT` and `EXCL` flags were provided.
     PathAlreadyExists,
+    ReadOnlyFileSystem,
     DeviceBusy,
     FileLocksUnsupported,
     /// One of these three things:

lib/std/Io/Threaded.zig

@@ -4290,6 +4290,7 @@ fn dirCreateFilePosix(
                         .AGAIN => return error.WouldBlock,
                         .TXTBSY => return error.FileBusy,
                         .NXIO => return error.NoDevice,
+                        .ROFS => return error.ReadOnlyFileSystem,
                         .ILSEQ => return error.BadPathName,
                         else => |err| return posix.unexpectedErrno(err),
                     }
@@ -4871,6 +4872,7 @@ fn dirOpenFilePosix(
                         .AGAIN => return error.WouldBlock,
                         .TXTBSY => return error.FileBusy,
                         .NXIO => return error.NoDevice,
+                        .ROFS => return error.ReadOnlyFileSystem,
                         .ILSEQ => return error.BadPathName,
                         else => |err| return posix.unexpectedErrno(err),
                     }

lib/std/Io/Uring.zig

@@ -5673,6 +5673,7 @@ fn openat(
             .AGAIN => return error.WouldBlock,
             .TXTBSY => return error.FileBusy,
             .NXIO => return error.NoDevice,
+            .ROFS => return error.ReadOnlyFileSystem,
             .ILSEQ => return error.BadPathName,
             else => |err| return unexpectedErrno(err),
         }

lib/std/debug/SelfInfo/Windows.zig

@@ -360,6 +360,7 @@ const Module = struct {
                 error.SystemFdQuotaExceeded,
                 error.FileLocksUnsupported,
                 error.FileBusy,
+                error.ReadOnlyFileSystem,
                 => return error.ReadFailed,
             };
             errdefer coff_file.close(io);

lib/std/zig/system.zig

@@ -423,6 +423,7 @@ pub fn resolveTargetQuery(io: Io, query: Target.Query) DetectError!Target {
         error.ConnectionResetByPeer => return error.Unexpected,
         error.NotOpenForReading => return error.Unexpected,
         error.SocketUnconnected => return error.Unexpected,
+        error.ReadOnlyFileSystem => return error.Unexpected,
 
         error.AccessDenied,
         error.SymLinkLoop,
@@ -853,6 +854,7 @@ fn glibcVerFromRPath(io: Io, rpath: []const u8) !std.SemanticVersion {
         error.PathAlreadyExists => return error.Unexpected, // read-only
         error.DeviceBusy => return error.Unexpected, // read-only
         error.FileBusy => return error.Unexpected, // read-only
+        error.ReadOnlyFileSystem => return error.Unexpected, // read-only
         error.NoDevice => return error.Unexpected, // not asking for a special device
         error.FileTooBig => return error.Unexpected,
         error.WouldBlock => return error.Unexpected, // not opened in non-blocking