win,fs: Fix compiler warnings and errors

* Use `DWORD` instead of `mode_t` on Windows. It's not needed to use `mode_t` here, and it just confuses VS.

* Define `S_IRWXU` and others if not already defined.

* When compiling on my windows testing box, I get the error:

```
error: initialization of 'SECURITY_INFORMATION' {aka 'long unsigned int'} from 'void *' makes integer from pointer without a cast [-Wint-conversion]
 2317 |   SECURITY_INFORMATION si = NULL;
```

src/win/fs.c

@@ -49,6 +49,23 @@
 #define UV_FS_FREE_PTR           0x0008
 #define UV_FS_CLEANEDUP          0x0010
 
+#ifndef S_IRWXU
+#define S_IRWXU                  0000700    /* RWX mask for owner */
+#define S_IRUSR                  0000400    /* R for owner */
+#define S_IWUSR                  0000200    /* W for owner */
+#define S_IXUSR                  0000100    /* X for owner */
+
+#define S_IRWXG                  0000070    /* RWX mask for group */
+#define S_IRGRP                  0000040    /* R for group */
+#define S_IWGRP                  0000020    /* W for group */
+#define S_IXGRP                  0000010    /* X for group */
+
+#define S_IRWXO                  0000007    /* RWX mask for other */
+#define S_IROTH                  0000004    /* R for other */
+#define S_IWOTH                  0000002    /* W for other */
+#define S_IXOTH                  0000001    /* X for other */
+#endif
+
 /* number of attempts to generate a unique directory name before declaring failure */
 #define TMP_MAX 32767
 
@@ -2120,7 +2137,7 @@ static void fs__access(uv_fs_t* req) {
 
   DWORD sdLen = 0, err = 0, tokenAccess = 0, desiredAccess = 0,
         grantedAccess = 0, privilegesLen = 0;
-  SECURITY_INFORMATION si = NULL;
+  SECURITY_INFORMATION si = (SECURITY_INFORMATION)NULL;
   PSECURITY_DESCRIPTOR sd = NULL;
   HANDLE hToken = NULL, hImpersonatedToken = NULL;
   GENERIC_MAPPING mapping = { 0xFFFFFFFF };
@@ -2242,7 +2259,7 @@ static void fs__access(uv_fs_t* req) {
 }
 
 static void build_access_struct(EXPLICIT_ACCESS_W* ea, PSID owner,
-                                TRUSTEE_TYPE user_type, mode_t mode_triplet,
+                                TRUSTEE_TYPE user_type, DWORD mode_triplet,
                                 ACCESS_MODE allow_deny) {
   /*
    * We map the typical POSIX mode bits r/w/x as the Windows
@@ -2305,7 +2322,7 @@ static void fs__chmod(uv_fs_t* req) {
        psidNull = NULL, psidCreatorGroup = NULL;
   PSECURITY_DESCRIPTOR pSD = NULL;
   PEXPLICIT_ACCESS_W ea = NULL, pOldEAs = NULL;
-  SECURITY_INFORMATION si = NULL;
+  SECURITY_INFORMATION si = (SECURITY_INFORMATION)NULL;
   DWORD numGroups = 0, tokenAccess = 0, u_mode = 0, g_mode = 0, o_mode = 0,
         u_deny_mode = 0, g_deny_mode = 0, attr = 0, new_attr = 0;
   HANDLE hToken = NULL, hImpersonatedToken = NULL;