patch 9.0.2013: confusing ifdefs in if_<lang>.c

Problem:  confusing ifdefs in if_<lang>.c
Solution: refactor ifndefs to #ifdefs

if_x: Avoid using #ifndef - #else - #endif

Using #ifndef - #else - #endif is sometimes confusing.
Use #ifdef - #else - #endif instead.

closes: #13310

Signed-off-by: Christian Brabandt <cb@256bit.org>
Co-authored-by: Ken Takata <kentkt@csc.jp>
diff --git a/src/if_lua.c b/src/if_lua.c
index 65d265f..159a675 100644
--- a/src/if_lua.c
+++ b/src/if_lua.c
@@ -102,18 +102,18 @@
 
 #ifdef DYNAMIC_LUA
 
-#ifndef MSWIN
+#ifdef MSWIN
+# define load_dll vimLoadLib
+# define symbol_from_dll GetProcAddress
+# define close_dll FreeLibrary
+# define load_dll_error GetWin32Error
+#else
 # include <dlfcn.h>
 # define HANDLE void*
 # define load_dll(n) dlopen((n), RTLD_LAZY|RTLD_GLOBAL)
 # define symbol_from_dll dlsym
 # define close_dll dlclose
 # define load_dll_error dlerror
-#else
-# define load_dll vimLoadLib
-# define symbol_from_dll GetProcAddress
-# define close_dll FreeLibrary
-# define load_dll_error GetWin32Error
 #endif
 
 // lauxlib