8139751: Javac crash with -XDallowStringFolding=false
Summary: When string folding is disabled, need to keep the original expression.
Reviewed-by: mcimadamore

8076543: Add @modules as needed to the langtools tests
Reviewed-by: jjg, shurailine

7068902: (javac) allow enabling or disabling of String folding
Summary: Contributed by netbeans team, modified to suit by the langtools team.
Reviewed-by: jjg, mcimadamore