In Mac OS X with Xcode 7.3, building java.desktop produces hundreds of lines of warnings like this:

/Users/dan/Dev/jdk/jdk9/jdk/src/java.desktop/macosx/native/libosxui/JRSUIConstantSync.m:132:5: warning: logical not is only applied to the left hand side of this comparison [-Wlogical-not-parentheses]
    CONSISTENCY_CHECK(Key, value);
    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/Users/dan/Dev/jdk/jdk9/jdk/src/java.desktop/macosx/native/libosxui/JRSUIConstantSync.m:96:10: note: expanded from macro 'CONSISTENCY_CHECK'
    if ( !CONSTANT_CHECK(clazz, constant) ) return NO;
         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/Users/dan/Dev/jdk/jdk9/jdk/src/java.desktop/macosx/native/libosxui/JRSUIConstantSync.m:132:5: note: add parentheses after the '!' to evaluate the comparison first

It appears innocent, but produces a lot of noise (and, if I configure without "--disable-warnings-as-errors", breaks the build).