RFR: JDK-8210960 Allow --with-boot-jdk-jvmargs to work during configure

Thu Sep 20 11:43:10 UTC 2018

Allow --with-boot-jdk-jvmargs to work during the configure phase. Also 
report the usages of _JAVA_OPTIONS and JAVA_TOOL_OPTIONS environment 
variables, which can seriously mess up the build.

Bug: https://bugs.openjdk.java.net/browse/JDK-8210960
WebRev: 
http://cr.openjdk.java.net/~ihse/JDK-8210960-use-with-boot-jdk-jvmargs-in-configure/webrev.01

/Magnus