Hi,

this patches fixes a 5/6 regression PR69426.

When compiling the test-case in the patch, the verify_ssa todo check 
fails after removing a clobber in eliminate_local_variables_stmt.

The problem is that the clobber is removed, but the uses of the 
corresponding vdef are not changed, and the virtual symbol is not marked 
for renaming.

[ The same happens in 4.9, but because omp_expand_local is called before 
verify_ssa, the ICE does not happen. In 5.0 and later, we use a separate 
expand_omp_ssa pass. ]

This patch fixes the problem by replacing the uses of the vdef of the 
clobber by the vuse of the clobber.

The patch uses replace_uses_by, but unlink_vdef_stmt also works, I'm not 
sure which one to use.

Bootstrapped and reg-tested on x86_64.

OK for trunk, gcc-5-branch?

Thanks,
- Tom