Mark Wielaard reports:

Can you explain the OPENJDK=true setting a bit more? I don't see it
mentioned at:
http://hg.openjdk.java.net/jdk7/build/raw-file/tip/README-builds.html#variables

I do see a Build Directives: OPENJDK = true in my build logs, but that
is not passed down to any subdir makes. Maybe it should be part of
COMMON_BUILD_ARGUMENTS in make/Defs-internal.gmk?

---

And later:

The simplest seems to be to at least add it to the
COMMON_BUILD_ARGUMENTS at the top-level like so:

--- openjdk/make/Defs-internal.gmk.orig 2012-10-03 16:08:00.239767294 +0200
+++ openjdk/make/Defs-internal.gmk 2012-10-03 16:07:50.508629201 +0200
@@ -325,6 +325,10 @@
     PREVIOUS_MICRO_VERSION=$(PREVIOUS_MICRO_VERSION) \
     STATIC_CXX=$(STATIC_CXX)
 
+ifdef OPENJDK
+ COMMON_BUILD_ARGUMENTS += OPENJDK=$(OPENJDK)
+endif
+
 ifdef ARCH_DATA_MODEL
   COMMON_BUILD_ARGUMENTS += ARCH_DATA_MODEL=$(ARCH_DATA_MODEL)
 endif

That works for my setup and should cover most default builds of openjdk
starting from the top-level.