Use --release flag to target intended JDK version

Starting with Java 9, the --release flag makes it possible to
compile Java code with a given version of the JDK but targeting an
earlier version of the Java API. The --source and --target flags alone
are not enough to guarantee this; the bootclasspath must also be set
appropriately, which the --release flag takes care of doing.

This change passes the value of the scijava.jvm.version property for
--release, as long as the version of Java being used is 9 or later.

With this enhancement, it is no longer necessary to restrict the
build environment (scijava.jvm.build.version) to Java 8 only.

Co-authored-by: Curtis Rueden <ctrueden@wisc.edu>

Author: axtimwalde

pom.xml

@@ -161,10 +161,10 @@
 		<license.copyrightOwners>N/A</license.copyrightOwners>
 
 		<!-- Compiler configuration. -->
-		<scijava.jvm.version>1.8</scijava.jvm.version>
+		<scijava.jvm.version>8</scijava.jvm.version>
 		<scijava.jvm.test.version>${scijava.jvm.version}</scijava.jvm.test.version>
 		<!-- NB: 1.8.0_101 is needed for SciJava Maven repository HTTPS support. -->
-		<scijava.jvm.build.version>[1.8.0-101,1.8.9999]</scijava.jvm.build.version>
+		<scijava.jvm.build.version>[1.8.0-101,)</scijava.jvm.build.version>
 		<maven.compiler.source>${scijava.jvm.version}</maven.compiler.source>
 		<maven.compiler.target>${scijava.jvm.version}</maven.compiler.target>
 		<maven.compiler.testSource>${scijava.jvm.test.version}</maven.compiler.testSource>
@@ -2015,5 +2015,14 @@
 				<scijava.platform.bits>32</scijava.platform.bits>
 			</properties>
 		</profile>
+		<profile>
+			<id>java-9</id>
+			<activation>
+				<jdk>[9,)</jdk>
+			</activation>
+			<properties>
+				<maven.compiler.release>${scijava.jvm.version}</maven.compiler.release>
+			</properties>
+		</profile>
 	</profiles>
 </project>