patch 7.4.1106

Problem:    The nsis script can't be used from the appveyor build.
Solution:   Add "ifndef" to allow for variables to be set from the command
            line. Remove duplicate SetCompressor command. Support using other
            gettext binaries. (Ken Takata)  Update build instructions to use
            libintl-8.dll.

src/os_w32exe.c

@@ -69,7 +69,7 @@ WinMain(
 
 #ifdef DYNAMIC_GETTEXT
     /* Initialize gettext library */
-    dyn_libintl_init(NULL);
+    dyn_libintl_init();
 #endif
 
 #ifdef VIMDLL