It appears that by default the ant build tool will sometimes pick up settings that impact the build from the environment and also from files like ~/.antrc, which will could invalidate settings needed in the jdk build process.

Use of --noconfig --nouserlib --noclasspath --noinput --autoproxy

The jars of the ant distribution need to be excluded too, but that may be well known, all javac logic in ant scripts needs to specify: includeAntRuntime="no"
Not doing this will result in many ant runtime jar files being included in your classpath.

Another issue is the poor ant tempdir logic, when using ant on the same system, it can easily collide with each other, so you need:
   export ANT_OPTS="-Djava.io.tmpdir='$(ANT_TMPDIR)'"
Where you have created a unique area for the ANT_TMPDIR.

Since there is no sharing of ant logic in the various repositories, every use of an ant build script needs to be checked.
Copied from http://bugs.openjdk.java.net/show_bug.cgi?id=100099

Description From Jesse Glick 2009-08-11 12:04:01 PDT

Created an attachment (id=129) [details]
Suggested patch

For clarity, use includeantruntime="false" on the compilation of make/tools
(consistent with other <javac> invocations in the same script); the classpath
already specifies ant.jar, which can also now be more robustly specified as
ant.core.lib (does not assume a particular layout of the Ant installation).

Helpful for using http://wiki.netbeans.org/AutomaticProjects on the langtools
project: File > New Project > Java > Automatic Project, select jdk7/langtools,
and when open Build and choose make/build.xml as the script (default target
selection 'build' is fine). Libraries node should show just ant.jar, not all
the other JARs in the Ant distribution and tools.jar.