RFR: JDK-8074554 Create custom hook for running after AC_OUTPUT

[Magnus Ihse Bursie]

The custom configure additions needs to be extended with a hook right 
after AC_OUTPUT.

Bug: https://bugs.openjdk.java.net/browse/JDK-8074554
Patch inlined:

diff --git a/common/autoconf/configure.ac b/common/autoconf/configure.ac
--- a/common/autoconf/configure.ac
+++ b/common/autoconf/configure.ac
@@ -54,6 +54,7 @@

  AC_DEFUN_ONCE([CUSTOM_EARLY_HOOK])
  AC_DEFUN_ONCE([CUSTOM_LATE_HOOK])
+AC_DEFUN_ONCE([CUSTOM_CONFIG_OUTPUT_GENERATED_HOOK])
  AC_DEFUN_ONCE([CUSTOM_SUMMARY_AND_WARNINGS_HOOK])

  # This line needs to be here, verbatim, after all includes and the 
dummy hook
@@ -264,6 +265,7 @@

  # Create the actual output files. Now the main work of configure is done.
  AC_OUTPUT
+CUSTOM_CONFIG_OUTPUT_GENERATED_HOOK

  # Try to move the config.log file to the output directory.
  if test -e ./config.log; then
magnusi at sthihse3:/localhome/hg/jdk9-client-EXP$

I intend to push this to jdk9/client, not jdk9/dev.

/Magnus