ARFLAGS needs a space

* configure.in (ARFLAGS): needs a trailing space to separate from
  the target library name, whereas VC linker flag must not
  separate from its argument.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@53800 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

configure.in

@@ -571,7 +571,7 @@ AC_CACHE_CHECK([for $AR D option], [rb_cv_ar_D_option], [
     AS_IF([$AR rcD conftest.a > /dev/null 2>&1 && rm conftest.a],
 	[rb_cv_ar_D_option=yes], [rb_cv_ar_D_option=no])
 ])
-AS_IF([test "$rb_cv_ar_D_option" = yes], [ARFLAGS=rcD], [ARFLAGS=rcu])
+AS_IF([test "$rb_cv_ar_D_option" = yes], [ARFLAGS='rcD '], [ARFLAGS='rcu '])
 AC_SUBST(ARFLAGS)
 
 AC_CHECK_TOOL(AS, as)