Fix latent bug in crossjumping

[Josef Zlomek]

> > gcc creates a reference to an undefined label when compiling the
> > attached testcase with "-O -fpic".
> 
> You're the man! :-)
> 
> If the fix is OK, you can close high priority PRs c/7887, java/8866, and
> java/8154.  Two hi-pri bugs gone!

If the patch gets approved I'll close the appropriate bug reports.

> Another suspects are c++/8819, and maybe c/7289 too, but for the latter
> unfortunately there is no test case to reproduce the bug :-/

Thanks for the PR numbers :-)
It must have taken you a long time to find them.

Josef