There are some changes in common-build that are wrong: The workaround for the Ant bug is exactly like that, that we pass "build.compiler=javac1.7" for every version >= 1.8, because Ant 1.8.3 and 1.8.4 have a bug, so we must pass javac1.7 (see link supplied in comment). So don't change that condition! Because we are now on minimum Java 8, you can set build.compiler always to javac1.7 as workaround:
<condition property="build.compiler" value="javac1.7">
<antversion exactly="1.8.3" />
<antversion exactly="1.8.4" />
Also some conditions/fails are commented out (also in root build.xml regarding smoke tester). The "needed minimum Java 8" <fail/> was commented out, why?