RFR: 8000461 Top level build doesn't pass OPENJDK=true through to the hotspot build

[David Holmes]

This is a simple fix contributed by Mark Weilaard to add the 
OPENJDK=true make variable to COMMON_BUILD_ARGUMENTS so that it gets 
passed down to the component builds - in particular hotspot:

http://cr.openjdk.java.net/~dholmes/8000461/webrev/

Here's an extract from a build log showing the value gets passed:

cd  ./hotspot/make && \
             make JDK_TOPDIR=/export/users/dh/jdk8-build/jdk 
JDK_MAKE_SHARED_DIR=/export/users/dh/jdk8-build/jdk/
make/common/shared EXTERNALSANITYCONTROL=true SOURCE_LANGUAGE_VERSION=7 
TARGET_CLASS_VERSION=7 MILESTONE=ea BUILD_NUMBER=b00
  JDK_BUILD_NUMBER=b00 FULL_VERSION=1.8.0-ea-b00 
PREVIOUS_JDK_VERSION=1.7.0 JDK_VERSION=1.8.0 JDK_MKTG_VERSION=8 JDK_MAJOR_VE
RSION=1 JDK_MINOR_VERSION=8 JDK_MICRO_VERSION=0 PREVIOUS_MAJOR_VERSION=1 
PREVIOUS_MINOR_VERSION=7 PREVIOUS_MICRO_VERSION=0 O
PENJDK=true ARCH_DATA_MODEL=64 COOKED_BUILD_NUMBER=0 
ALT_OUTPUTDIR=/export/users/dh/jdk8-build/builds/b00/openjdk-linu
x-i586-ea/hotspot/outputdir 
ALT_EXPORT_PATH=/export/users/dh/jdk8-build/builds/b00/openjdk-linux-i586-ea/hotspot/impor
t BUILD_FLAVOR=product ALT_SLASH_JAVA=/java 
ALT_BOOTDIR=/java/re/jdk/1.7.0/archive/fcs/binaries/linux-amd64 
ALT_LANGTOOLS_DI
ST=/export/users/dh/jdk8-build/builds/b00/openjdk-linux-i586-ea/langtools/dist 
all_product

Thanks,
David