RFR: JDK-8198627 JDK-8198318 broke readlink testing

[Magnus Ihse Bursie]

The if line introduced in JDK-8198318 is missing a "test".
Thanks to Jon and Erik for discovering the problem and the solution.

Bug: https://bugs.openjdk.java.net/browse/JDK-8198627
Patch inline:

diff --git a/make/autoconf/basics.m4 b/make/autoconf/basics.m4
--- a/make/autoconf/basics.m4
+++ b/make/autoconf/basics.m4
@@ -263,7 +263,7 @@
        READLINK_TESTED=yes
      fi

-    if test "x$READLINK" != x && "x$READLINK_ISGNU" != x; then
+    if test "x$READLINK" != x && test "x$READLINK_ISGNU" != x; then
        $1=`$READLINK -f [$]$1`
      else
        # Save the current directory for restoring afterwards

/Magnus