[C++] PATCH to build_vec_init for c++/12253

[Gabriel Dos Reis]

Jason Merrill <jason@redhat.com> writes:

| We were failing to destroy temporaries after initializing an array element
| from an initializer list.  This is a semantic bug on the trunk (and at
| least back to 2.95), as well as causing a crash on the tree-ssa branch.
| 
| Tested on x86_64-pc-linux-gnu, applied to trunk and tree-ssa.  Gaby, shall
| I apply this to the 3.3 branch as well?

Yes. Thank you very much.

-- Gaby