The Merlin installation bundles on Windows are broken. One manifestation
of this is that they don't install plugin. There may be even more to it,
because it looks like the JRE bundle, for instance, is only half the size
it ought to be.

The build log contains this:

../../../build/win32/bin/java -classpath ../../../build/win32/tmp/ishield/../sun.tools.crunch sun.tools.crunch.Crunch ../../../build/win32/tmp/ishield/rt.jar > ../../../build/win32/tmp/ishield/rt.log
Processing class files
java.io.IOException: Unexpected classfile major version 46
        at sun.tools.crunch.ClassFile.<init>(ClassFile.java:70)
        at sun.tools.crunch.ClassFile.read(ClassFile.java:51)
        at sun.tools.crunch.Crunch.doit(Crunch.java:199)
        at sun.tools.crunch.Crunch.main(Crunch.java:281)

Neal writes:

That one's easy. The latest TL putback incremented the default
javac -target to 1.2. That's classfile version 46.0.
Our tools should be prepared to handle class files up
through 48.0.

See bugid 4393930.