need shell's escape instead of M4's.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@62224 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

tool/m4/ruby_check_va_copy.m4

@@ -24,7 +24,7 @@ main()
     conftest(10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0);
     exit(0);
 }],
-	rb_cv_va_copy=[$1],
+	rb_cv_va_copy="$1",
         rb_cv_va_copy="",
         rb_cv_va_copy="")dnl
     fi