RFR: JDK-8179361 specify -javafx option for javadoc command

[Magnus Ihse Bursie]

If doclint is enabled for the javadoc command, it shows a bunch of 119 
errors for "unknown tag @defaultValue". This means that javadoc is not 
correctly processing the tag to generate the correct documentation.

This tag is currently enabled by the -javafx option.

Eventually, we should review JavaFX support in javadoc, but for now the 
best solution to these errors is to use the -javafx option in the 
javadoc command.

Bug: https://bugs.openjdk.java.net/browse/JDK-8179361
Patch inline:
diff --git a/make/Javadoc.gmk b/make/Javadoc.gmk
--- a/make/Javadoc.gmk
+++ b/make/Javadoc.gmk
@@ -91,7 +91,7 @@
  # The initial set of options for javadoc
  JAVADOC_OPTIONS := -XDignore.symbol.file=true -use -keywords 
-notimestamp \
      -serialwarn -encoding ISO-8859-1 -breakiterator -splitIndex 
--system none \
-    -html5 --expand-requires transitive
+    -html5 -javafx --expand-requires transitive

  # Should we add DRAFT stamps to the generated javadoc?
  ifeq ($(VERSION_IS_GA), true)

/Magnus