fix: complie errors

include/os/osString.h

@@ -22,7 +22,7 @@ extern "C" {
 
 typedef wchar_t TdWchar;
 typedef int32_t TdUcs4;
-#ifndef DISALLOW_NCHAR_WITHOUT_ICONV
+#if !defined(DISALLOW_NCHAR_WITHOUT_ICONV) && defined(DARWIN)
 #include "iconv.h"
 #else
 typedef void   *iconv_t;

source/os/src/osString.c

@@ -17,6 +17,10 @@
 #define _DEFAULT_SOURCE
 #include "os.h"
 
+#ifndef DISALLOW_NCHAR_WITHOUT_ICONV
+#include "iconv.h"
+#endif
+
 extern int wcwidth(wchar_t c);
 extern int wcswidth(const wchar_t *s, size_t n);