Fix wasi::fs::OpenOptions to imply write when append is on

Author: kawamuray

Diff for: library/std/src/sys/wasi/fs.rs

@@ -46,6 +46,7 @@ pub struct DirEntry {
 pub struct OpenOptions {
     read: bool,
     write: bool,
+    append: bool,
     dirflags: wasi::Lookupflags,
     fdflags: wasi::Fdflags,
     oflags: wasi::Oflags,
@@ -270,8 +271,9 @@ impl OpenOptions {
         }
     }
 
-    pub fn append(&mut self, set: bool) {
-        self.fdflag(wasi::FDFLAGS_APPEND, set);
+    pub fn append(&mut self, append: bool) {
+        self.append = append;
+        self.fdflag(wasi::FDFLAGS_APPEND, append);
     }
 
     pub fn dsync(&mut self, set: bool) {
@@ -321,7 +323,7 @@ impl OpenOptions {
             base |= wasi::RIGHTS_FD_READ;
             base |= wasi::RIGHTS_FD_READDIR;
         }
-        if self.write {
+        if self.write || self.append {
             base |= wasi::RIGHTS_FD_WRITE;
             base |= wasi::RIGHTS_FD_DATASYNC;
             base |= wasi::RIGHTS_FD_ALLOCATE;