examples: Quote shell variables in hello-java*/configure
When running from xsmallpot.sh, embedded shell-script snippets are
stripped off from configure.ac and some variables are not set.
Make sure to quote them to avoid error.
* hello-java/configure.ac: Quote $BUILDJAVA.
* hello-java-awt/configure.ac: Quote $BUILDJAVAEXE and $BUILDJAVA.
* hello-java-qtjambi/configure.ac: Likewise.
* hello-java-swing/configure.ac: Likewise.
