libc. Add basic wchar.h

libc/include/wchar.h

@@ -0,0 +1,25 @@
+/* wchar.h: Wide-character string manipulation functions. */
+
+#ifndef _WCHAR_H
+#define _WCHAR_H
+
+typedef long int wint_t;
+
+#include <stddef.h>
+
+#ifdef __cplusplus
+extern "C"
+{
+#endif
+
+    /* Calculate the size of a null-terminated wide character string. */
+    size_t wcslen(const wchar_t* str);
+
+    /* Compare two null-terminated wide character strings. */
+    int wcscmp(const wchar_t* a, const wchar_t* b);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif