Makefile.sub: va_copy in old version

* win32/Makefile.sub: va_copy is available since VS12 (VC 18.00).
  simple copy same as VC1 19.00.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@62223 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

win32/Makefile.sub

@@ -618,7 +618,11 @@ $(CONFIG_H): $(MKFILES) $(srcdir)/win32/Makefile.sub $(win_srcdir)/Makefile.sub
 #define HAVE_PROTOTYPES 1
 #define TOKEN_PASTE(x,y) x##y
 #define HAVE_STDARG_PROTOTYPES 1
+!if $(MSC_VER) >= 1800
 #define HAVE_VA_COPY 1
+!else
+#define HAVE_VA_COPY_VIA_STRUCT_ASSIGNMENT 1
+!endif
 !if $(MSC_VER) > 1100
 #define NORETURN(x) __declspec(noreturn) x
 !endif