configure.in: escape double-quotes

* configure.in (unexpand_shvar): escape double-quotes in backquotes in
  double-quotes for some shells.  [Bug #7959]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@39525 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

configure.in

@@ -3286,7 +3286,7 @@ unexpand_shvar() {
     test "$#" -eq 0 && return
     for n do
         eval v='"$'$n'"'
-	v="`echo \"$v\" | sed -e ['s/${[^${}"]*}/"&"/g'] -e ['s/[][$|.\\?*]/\\\\&/g']`"
+	v="`echo \"$v\" | sed -e ['s/${[^${}\"]*}/\"&\"/g'] -e ['s/[][$|.\\?*]/\\\\&/g']`"
 	if test -n "$v"; then
 	    expr=["${expr};s|"'\("[^$"]*\)'"$v|\\1\${$n}\"|g"]
 	    AS_CASE(["$v"], [*'${'*'}'*], [expr=["$expr;s|$v|\"\${$n}\"|g"]])