It is still important for some clients that JDK 8 langtools repo can be built with JDK 6. 7151010 introduced some unnecessary dependencies on JDK 7, which should be removed.
[javac] /w/jjg/work/type-annos/8/langtools.NNNNNNN.jdk6/src/share/classes/com/sun/tools/javac/comp/Annotate.java:29: cannot find symbol
    [javac] symbol : class Objects
    [javac] location: package java.util
    [javac] import java.util.Objects;
    [javac] ^
    [javac] /w/jjg/work/type-annos/8/langtools.NNNNNNN.jdk6/src/share/classes/com/sun/tools/javac/comp/Annotate.java:154: cannot find symbol
    [javac] symbol : variable Objects
    [javac] location: class com.sun.tools.javac.comp.Annotate.AnnotateRepeatedContext
    [javac] Objects.requireNonNull(env);
    [javac] ^
    [javac] /w/jjg/work/type-annos/8/langtools.NNNNNNN.jdk6/src/share/classes/com/sun/tools/javac/comp/Annotate.java:155: cannot find symbol
    [javac] symbol : variable Objects
    [javac] location: class com.sun.tools.javac.comp.Annotate.AnnotateRepeatedContext
    [javac] Objects.requireNonNull(annotated);
    [javac] ^
    [javac] /w/jjg/work/type-annos/8/langtools.NNNNNNN.jdk6/src/share/classes/com/sun/tools/javac/comp/Annotate.java:156: cannot find symbol
    [javac] symbol : variable Objects
    [javac] location: class com.sun.tools.javac.comp.Annotate.AnnotateRepeatedContext
    [javac] Objects.requireNonNull(pos);
    [javac] ^
    [javac] /w/jjg/work/type-annos/8/langtools.NNNNNNN.jdk6/src/share/classes/com/sun/tools/javac/comp/Annotate.java:157: cannot find symbol
    [javac] symbol : variable Objects
    [javac] location: class com.sun.tools.javac.comp.Annotate.AnnotateRepeatedContext
    [javac] Objects.requireNonNull(log);
    [javac] ^
    [javac] 5 errors