When building with --enable-sjavac, I get this (on jdk9-dev repo):

## Starting langtools
Compiling 1 files for BUILD_TOOLS
Compiling 33 properties into resource bundles
Compiling 788 files for BUILD_INTERIM_LANGTOOLS
Creating langtools/dist/interim_langtools.jar
Updating langtools/dist/lib/src.zip
Compiling BUILD_FULL_LANGTOOLS
/w/lt/9/dev/langtools/src/share/classes/com/sun/tools/javac/model/AnnotationProxyMaker.java:87: warning: AnnotationParser is internal proprietary API and may be removed in a future release
        return AnnotationParser.annotationForMap(annoType,
               ^
/w/lt/9/dev/langtools/src/share/classes/com/sun/tools/javac/model/AnnotationProxyMaker.java:166: warning: ExceptionProxy is internal proprietary API and may be removed in a future release
            if (!(value instanceof ExceptionProxy) &&
                                   ^
/w/lt/9/dev/langtools/src/share/classes/com/sun/tools/javac/model/AnnotationProxyMaker.java:167: warning: AnnotationType is internal proprietary API and may be removed in a future release
                !AnnotationType.invocationHandlerReturnType(returnClass)
                 ^
/w/lt/9/dev/langtools/src/share/classes/com/sun/tools/javac/model/AnnotationProxyMaker.java:203: warning: ExceptionProxy is internal proprietary API and may be removed in a future release
                        if (value == null || value instanceof ExceptionProxy) {
                                                              ^
/w/lt/9/dev/langtools/src/share/classes/com/sun/tools/javac/model/AnnotationProxyMaker.java:227: warning: EnumConstantNotPresentExceptionProxy is internal proprietary API and may be removed in a future release
                    value = new EnumConstantNotPresentExceptionProxy(
                                ^
/w/lt/9/dev/langtools/src/share/classes/com/sun/tools/javac/model/AnnotationProxyMaker.java:257: warning: ExceptionProxy is internal proprietary API and may be removed in a future release
            class AnnotationTypeMismatchExceptionProxy extends ExceptionProxy {
                                                               ^
/w/lt/9/dev/langtools/src/share/classes/com/sun/tools/javac/model/AnnotationProxyMaker.java:281: warning: ExceptionProxy is internal proprietary API and may be removed in a future release
    private static final class MirroredTypeExceptionProxy extends ExceptionProxy {
                                                                  ^
/w/lt/9/dev/langtools/src/share/classes/com/sun/tools/javac/model/AnnotationProxyMaker.java:324: warning: ExceptionProxy is internal proprietary API and may be removed in a future release
    private static final class MirroredTypesExceptionProxy extends ExceptionProxy {
                                                                   ^
error: warnings found and -Werror specified
1 error
8 warnings

Used to work before. Could be related to this JDK-8046369 ?