RFR: JDK-8244210: The javac server is never used

[Erik Joelsson]

Hello,

A minor mistake in JDK-8244036 is causing the javac server to never be 
used, which is rather severly increasing build times.

Before that change, the global variable ENABLE_SJAVAC was used to 
determine if the server should be activated. After the change, the 
global variable has changed names to ENABLE_JAVAC_SERVER. The 
conditional in JavaCompilation.gmk tries to check the value of the local 
variable/parameter $1_ENABLE_JAVAC_SERVER instead, but this parameter is 
never set or given a default. I don't think we need a local 
variable/parameter for this as there is currently no need to disable the 
server for any specific SetupJavaCompilation call, so I my fix is to 
just refer directly to the global variable from configure/spec.gmk instead.

Bug: https://bugs.openjdk.java.net/browse/JDK-8244210

Webrev: http://cr.openjdk.java.net/~erikj/8244210/webrev.01/webrev/

/Erik