RFR: JDK-8140277 Configuration out-of-date check should also check closed sources

[Magnus Ihse Bursie]

In Init.gmk, there is a check if the configure source code has changes. 
If so, the configuration is out of date and not usable.

This check should be extended to the closed configuration sources (if 
present), not only open.

The CUSTOM_CONFIG_DIR is the same as what's being used in 
common/autoconf/configure and common/autoconf/autogen.sh.

Bug: https://bugs.openjdk.java.net/browse/JDK-8140277

Patch inline:
diff --git a/make/Init.gmk b/make/Init.gmk
--- a/make/Init.gmk
+++ b/make/Init.gmk
@@ -137,7 +137,9 @@

      # The spec files depend on the autoconf source code. This check 
makes sure
      # the configuration is up to date after changes to configure.
-    $(SPECS): $(wildcard $(topdir)/common/autoconf/*)
+    CUSTOM_CONFIG_DIR ?= $(topdir)/closed/autoconf
+
+    $(SPECS): $(wildcard $(topdir)/common/autoconf/*) $(wildcard 
$(CUSTOM_CONFIG_DIR)/*)
          ifeq ($(CONF_CHECK), fail)
           @echo "Error: The configuration is not up to date for 
'$(lastword $(subst /, , $(dir $@)))'."
           $(call PrintConfCheckFailed)

/Magnus