RFR: JDK-8074554 Create custom hook for running after AC_OUTPUT (8u backport)

[Magnus Ihse Bursie]

Please review this backport of JDK-8074554 to 8u. While it did not 
automatically apply cleanly, the difference was trivially resolved.

diff --git a/common/autoconf/configure.ac b/common/autoconf/configure.ac
--- a/common/autoconf/configure.ac
+++ b/common/autoconf/configure.ac
@@ -53,6 +53,7 @@

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

  # This line needs to be here, verbatim, after all includes and the 
dummy hook
  # definitions. It is replaced with custom functionality when building
@@ -237,6 +238,7 @@

  # 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

/Magnus