fix: reject opening directories as files in ext2 and fat32, add mbrtowc to libc

programs/lib/libc/libc.c

@@ -25,6 +25,7 @@
 #include <sys/mman.h>
 #include <sys/time.h>
 #include <unistd.h>
+#include <wchar.h>
 
 /* ========================================================================
    Raw syscall wrappers (C versions matching kernel ABI)
@@ -3622,6 +3623,20 @@ int mbtowc(wchar_t *pwc, const char *s, size_t n) {
     return 1;
 }
 
+/* Restartable form of mbtowc. The C locale carries no shift state, so ps is
+   ignored; binutils reaches for this once configure sees mbstate_t. */
+size_t mbrtowc(wchar_t *pwc, const char *s, size_t n, mbstate_t *ps) {
+    (void)ps;
+    if (s == NULL) return 0;         /* query: the C locale is stateless */
+    if (n == 0) return (size_t)-2;   /* incomplete: no bytes to examine */
+    if (*s == '\0') {
+        if (pwc != NULL) *pwc = 0;
+        return 0;
+    }
+    if (pwc != NULL) *pwc = (wchar_t)(unsigned char)*s;
+    return 1;
+}
+
 int wctomb(char *s, wchar_t wc) {
     if (s == NULL) return 0;
     *s = (char)wc;