patch 7.4.1065

Problem:    Cannot use the "dll" options on MS-Windows.
Solution:   Support the options on all platforms.  Use the built-in name as
            the default, so that it's clear what Vim is looking for.

src/if_python3.c

@@ -686,12 +686,7 @@ py3_runtime_link_init(char *libname, int verbose)
     int
 python3_enabled(int verbose)
 {
-#ifdef WIN3264
-    char *dll = DYNAMIC_PYTHON3_DLL;
-#else
-    char *dll = *p_py3dll ? (char *)p_py3dll : DYNAMIC_PYTHON3_DLL;
-#endif
-    return py3_runtime_link_init(dll, verbose) == OK;
+    return py3_runtime_link_init((char *)p_py3dll, verbose) == OK;
 }
 
 /* Load the standard Python exceptions - don't import the symbols from the