Assert error on ambiguous fstflags

This commit adds a Rust test case that asserts an ambiguous `fstflags`
input to `fd_filestat_set_times` should result in `inval` errno.
An `fstflags` argument is ambiguous if:

1. both `atim` and `atim_now` are set, or
2. both `mtim` and `mtim_now` are set.

tests/rust/src/bin/fstflags_validate.rs

@@ -0,0 +1,57 @@
+use std::{env, process};
+use wasi_tests::open_scratch_directory;
+
+unsafe fn test_fstflags_validate(dir_fd: wasi::Fd) {
+    const FILE_NAME: &str = "fstflags_validate.cleanup";
+
+    let file_fd = wasi::path_open(
+        dir_fd,
+        0,
+        FILE_NAME,
+        wasi::OFLAGS_CREAT,
+        wasi::RIGHTS_FD_READ | wasi::RIGHTS_FD_FILESTAT_SET_TIMES,
+        0,
+        0,
+    )
+    .expect("failed to create file");
+
+    let result = wasi::fd_filestat_set_times(
+        file_fd,
+        100,
+        200,
+        wasi::FSTFLAGS_MTIM | wasi::FSTFLAGS_MTIM_NOW,
+    );
+    assert!(matches!(result, Err(wasi::ERRNO_INVAL)));
+
+    let result = wasi::fd_filestat_set_times(
+        file_fd,
+        100,
+        200,
+        wasi::FSTFLAGS_ATIM | wasi::FSTFLAGS_ATIM_NOW,
+    );
+    assert!(matches!(result, Err(wasi::ERRNO_INVAL)));
+
+    wasi::fd_close(file_fd).expect("failed to close fd");
+}
+fn main() {
+    let mut args = env::args();
+    let prog = args.next().unwrap();
+    let arg = if let Some(arg) = args.next() {
+        arg
+    } else {
+        eprintln!("usage: {} <scratch directory>", prog);
+        process::exit(1);
+    };
+
+    // Open scratch directory
+    let dir_fd = match open_scratch_directory(&arg) {
+        Ok(dir_fd) => dir_fd,
+        Err(err) => {
+            eprintln!("{}", err);
+            process::exit(1)
+        }
+    };
+
+    // Run the tests.
+    unsafe { test_fstflags_validate(dir_fd) }
+}

tests/rust/testsuite/fstflags_validate.json

@@ -0,0 +1,4 @@
+{
+    "dirs": ["fs-tests.dir"],
+    "args": ["fs-tests.dir"]
+}