[WasmFS] Ignore rather than asserting on O_NONBLOCK (#19084)

O_NONBLOCK serves two purposes when passed to open. First, it prevents `open`
from blocking for a "long time" to open the file. Second, it opens the file in
nonblocking I/O mode which allows reads and writes to return error codes if I/O
cannot be done without blocking. Ignoring O_NONBLOCK completely is a
semantically valid implementation strategy, so for now just stop asserting when
it is used.

Author: tlively

system/lib/wasmfs/syscalls.cpp

@@ -418,9 +418,9 @@ static __wasi_fd_t doOpen(path::ParsedParent parsed,
   }
 
   // TODO: remove assert when all functionality is complete.
-  assert((flags &
-          ~(O_CREAT | O_EXCL | O_DIRECTORY | O_TRUNC | O_APPEND | O_RDWR |
-            O_WRONLY | O_RDONLY | O_LARGEFILE | O_NOFOLLOW | O_CLOEXEC)) == 0);
+  assert((flags & ~(O_CREAT | O_EXCL | O_DIRECTORY | O_TRUNC | O_APPEND |
+                    O_RDWR | O_WRONLY | O_RDONLY | O_LARGEFILE | O_NOFOLLOW |
+                    O_CLOEXEC | O_NONBLOCK)) == 0);
 
   if (auto err = parsed.getError()) {
     return err;