FindJava: Add support for OpenJDK early access builds

OpenJDK 9 early access builds use a version string of "9-ea", and
locally built installations use "9-internal", neither of which is
currently accepted by the FindJava macro.  Map those versions to "1.9".
If the final released version is "9.0" the version interpretation could
be changed to match at that time.

Modules/FindJava.cmake

@@ -143,6 +143,9 @@ if(Java_JAVA_EXECUTABLE)
       if(var MATCHES "java version \"([0-9]+\\.[0-9]+\\.[0-9_.]+.*)\"")
         # This is most likely Sun / OpenJDK, or maybe GCJ-java compat layer
         set(Java_VERSION_STRING "${CMAKE_MATCH_1}")
+      elseif(var MATCHES "openjdk version \"([0-9]+)-[a-z]+\"")
+        # OpenJDK 9 early access builds or locally built
+        set(Java_VERSION_STRING "1.${CMAKE_MATCH_1}.0")
       elseif(var MATCHES "java full version \"kaffe-([0-9]+\\.[0-9]+\\.[0-9_]+)\"")
         # Kaffe style
         set(Java_VERSION_STRING "${CMAKE_MATCH_1}")