When building jdk11u-dev on a Linux ppc64le machine with OpenJDK8 installed, I get the following message :

configure: Found potential Boot JDK using java(c) in PATH
configure: Potential Boot JDK found at /usr/lib/jvm/java-8-openjdk-ppc64el is incorrect JDK version (openjdk version "1.8.0_292"); ignoring
configure: (Your Boot JDK version must be one of: 10 11)
configure: Found potential Boot JDK using well-known locations (in /usr/lib/jvm/java-8-openjdk-ppc64el)
configure: Potential Boot JDK found at /usr/lib/jvm/java-8-openjdk-ppc64el is incorrect JDK version (openjdk version "1.8.0_292"); ignoring
configure: (Your Boot JDK version must be one of: 10 11)
configure: Found potential Boot JDK using well-known locations (in /usr/lib/jvm/java-11-openjdk-ppc64el)
configure: Potential Boot JDK found at /usr/lib/jvm/java-11-openjdk-ppc64el did not contain bin/javac; ignoring
configure: (This might be an JRE instead of an JDK)
configure: Found potential Boot JDK using well-known locations (in /usr/lib/jvm/java-1.8.0-openjdk-ppc64el)
configure: Potential Boot JDK found at /usr/lib/jvm/java-1.8.0-openjdk-ppc64el is incorrect JDK version (openjdk version "1.8.0_292"); ignoring
configure: (Your Boot JDK version must be one of: 10 11)
configure: Found potential Boot JDK using well-known locations (in /usr/lib/jvm/java-1.11.0-openjdk-ppc64el)
configure: Potential Boot JDK found at /usr/lib/jvm/java-1.11.0-openjdk-ppc64el did not contain bin/javac; ignoring
configure: (This might be an JRE instead of an JDK)
configure: Found potential Boot JDK using well-known locations (in /usr/lib/jvm/default-java)
configure: Potential Boot JDK found at /usr/lib/jvm/default-java did not contain bin/javac; ignoring
configure: (This might be an JRE instead of an JDK)
configure: Could not find a valid Boot JDK. You might be able to fix this by running 'sudo apt-get install openjdk-8-jdk'.
configure: This might be fixed by explicitly setting --with-boot-jdk
configure: error: Cannot continue
configure exiting with result code 1

I think the help output should better mention openjdk-11-jdk because 8 is not sufficient to build jdk11.