PR36055: fix computation of *-dependence in nested initializer lists.

When we synthesize an implicit inner initializer list when analyzing an outer
initializer list, we add it to the outer list immediately, and then fill in the
inner list. This gives the outer list no chance to update its *-dependence bits
with those of the completed inner list. To fix this, re-add the inner list to
the outer list once it's completed.

Note that we do not recompute the *-dependence bits from scratch when we
complete an outer list; this would give the wrong result for the case where a
designated initializer overwrites a dependent initializer with a non-dependent
one. The resulting list in that case should still be dependent, even though all
traces of the dependence were removed from the semantic form.

llvm-svn: 324537