[committed] Backports to 9.x branch

Hi! I've backported these 15 commits from trunk to 9.x branch, bootstrapped/regtested them on x86_64-linux and i686-linux and committed. Jakub PR c++/92992 * call.c (convert_arg_to_ellipsis): For decltype(nullptr) arguments that have side-effects use cp_build_compo

Backports to 9.x

Hi! I've backported following 25 patches from trunk to 9.x, bootstrapped/regtested on x86_64-linux and i686-linux, committed to gcc-9-branch. Jakub 2019-12-20 Jakub Jelinek Backported from mainline 2019-11-21 Jakub Jelinek Jason Merrill