LibC: Implement mblen()

Author: https://github.com/gmta
Commit: https://github.com/SerenityOS/serenity/commit/0e990a4be89
Pull-request: https://github.com/SerenityOS/serenity/pull/7757

Userland/Libraries/LibC/stdlib.cpp

@@ -865,6 +865,14 @@ lldiv_t lldiv(long long numerator, long long denominator)
     return result;
 }
 
+int mblen(char const* s, size_t n)
+{
+    // FIXME: Implement locale support
+    if (!s)
+        return 0;
+    return (MB_CUR_MAX > n) ? n : MB_CUR_MAX;
+}
+
 size_t mbstowcs(wchar_t*, const char*, size_t)
 {
     dbgln("FIXME: Implement mbstowcs()");

Userland/Libraries/LibC/stdlib.h

@@ -59,6 +59,7 @@ char* mktemp(char*);
 int mkstemp(char*);
 char* mkdtemp(char*);
 void* bsearch(const void* key, const void* base, size_t nmemb, size_t size, int (*compar)(const void*, const void*));
+int mblen(char const*, size_t);
 size_t mbstowcs(wchar_t*, const char*, size_t);
 int mbtowc(wchar_t*, const char*, size_t);
 int wctomb(char*, wchar_t);