Dear all,

while analyzing several issues involving constructors and constant
array expressions, such as in PR102717 and PR102787, a common problem
showed up: we did not always properly expand parameter arrays,
array sections, or sections with vector subscripts.

Besides several ICEs as in these PRs, the incomplete expansion
led to an unnecessary creation of array temporaries.  This is
improved by the attached patch.

Regtested on x86_64-pc-linux-gnu.

OK for mainline?

Thanks,
Harald