Fix getenv() declaration compatibility issue

Remove old-style extern declaration that conflicts with stdlib.h.
This fixes compilation error with modern GCC versions.

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

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

w3mbookmark.c

@@ -9,9 +9,9 @@
 
 #if LANG == JA
 /* FIXME: gettextize here */
-#define BKMARK_TITLE "<22>֥å<D6A5><C3A5>ޡ<EFBFBD><DEA1><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ͽ"
-#define BKMARK_ADD "<22><>Ͽ"
-#define DEFAULT_SECTION "̤ʬ<CCA4><CAAC>"
+#define BKMARK_TITLE "<22>֥å<D6A5><C3A5>ޡ<EFBFBD><DEA1><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ͽ"
+#define BKMARK_ADD "<22><>Ͽ"
+#define DEFAULT_SECTION "̤ʬ<CCA4><CAAC>"
 #else
 #define BKMARK_TITLE "Register to my bookmark"
 #define BKMARK_ADD "ADD"
@@ -183,7 +183,6 @@ insert_bookmark(char *bmark, struct parsed_tagarg *data)
 int
 main(void)
 {
-    extern char *getenv();
     char *p;
     int length;
     Str qs = NULL;