Fix warnings

znz · znz · commit eba90bc03482 · 2022-01-20T10:03:59.000+09:00
```
compiling ..../ruby/ruby/dln.c
..../ruby/ruby/dln.c:108:1: warning: unused function 'init_funcname_len' [-Wunused-function]
init_funcname_len(const char **file)
^
..../ruby/ruby/dln.c:122:19: warning: unused variable 'funcname_prefix' [-Wunused-const-variable]
static const char funcname_prefix[sizeof(FUNCNAME_PREFIX) - 1] = FUNCNAME_PREFIX;
		  ^
2 warnings generated.
```
diff --git a/dln.c b/dln.c
@@ -104,6 +104,7 @@ dln_loaderror(const char *format, ...)
 #define isdirsep(x) ((x) == '/')
 #endif
 
+#if defined(_WIN32) || defined(USE_DLN_DLOPEN)
 static size_t
 init_funcname_len(const char **file)
 {
@@ -134,6 +135,7 @@ static const char funcname_prefix[sizeof(FUNCNAME_PREFIX) - 1] = FUNCNAME_PREFIX
     tmp[plen+flen] = '\0';\
     *(buf) = tmp;\
 } while (0)
+#endif
 
 #ifdef USE_DLN_DLOPEN
 # include <dlfcn.h>
