I recloned hg.openjdk.java.net/jdk7u/jdk7u-dev/jdk today and the build failed as follows:
make[3]: Entering directory `/cygdrive/c/Users/Pete/JDK7u/jdk7u-dev/jdk/make/com/sun/jmx' /usr/bin/mkdir -p ../../../../build/windows-i586/classes/javax/management/remote/rmi rm -f ../../../../build/windows-i586/classes/javax/management/remote/rmi/RMIConnectionImpl_Stub.class ../../../../build/windows-i586/bin/java -XX:-PrintVMOptions -XX:+UnlockDiagnosticVMOptions -XX:-LogVMOutput -client -Xmx512m -Xms512m -XX:PermSize=32m -XX:MaxPermSize=160m -cp ../../../../build/windows-i586/classes sun.rmi.rmic.Main -classpath "../../../../build/windows-i586/classes" \ -d ../../../../build/windows-i586/classes \ -v1.2 \ -keepgenerated \ javax.management.remote.rmi.RMIConnectionImpl Error occurred during initialization of VM java/lang/NoClassDefFoundError: java/lang/invoke/AdapterMethodHandle make[3]: *** [../../../../build/windows-i586/classes/javax/management/remote/rmi/RMIConnectionImpl_Stub.class] Error 1 make[3]: Leaving directory `/cygdrive/c/Users/Pete/JDK7u/jdk7u-dev/jdk/make/com/sun/jmx'