Fix getenv() declaration in w3mhelperpanel.c

Remove old-style extern declaration that conflicts with stdlib.h.
Continues modernization for GCC compatibility.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

w3mhelperpanel.c

@@ -12,13 +12,13 @@
 
 #if LANG == JA
 /* FIXME: gettextize here */
-#define MSG_TITLE		"外部ビューアの編集"
-#define MSG_NEW_ENTRY		"新規登録"
-#define MSG_TYPE		"データタイプ"
-#define MSG_COMMAND		"外部コマンド"
-#define MSG_REGISTER		"登録"
-#define MSG_DELETE		"削除"
-#define MSG_DOIT		"実行"
+#define MSG_TITLE		"<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ӥ塼<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Խ<EFBFBD>"
+#define MSG_NEW_ENTRY		"<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ͽ"
+#define MSG_TYPE		"<EFBFBD>ǡ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>"
+#define MSG_COMMAND		"<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ޥ<EFBFBD><EFBFBD>"
+#define MSG_REGISTER		"<EFBFBD><EFBFBD>Ͽ"
+#define MSG_DELETE		"<EFBFBD><EFBFBD><EFBFBD>"
+#define MSG_DOIT		"<EFBFBD>¹<EFBFBD>"
 #else				/* LANG != JA */
 #define MSG_TITLE		"External Viewers Setup"
 #define MSG_NEW_ENTRY		"New Entry"
@@ -167,7 +167,6 @@ int
 main(void)
 {
     Str mailcapfile;
-    extern char *getenv();
     char *p;
     int length;
     Str qs = NULL;