GNU: C++23 support

Added in GCC commit 78739c2df788ee5c868d998a6333d453317d8711, released in 11.1.
No lettered variant beforehand this time around.

Implements #22139.
36 jobs for !6108 with cpp23_gcc in 6 minutes and 53 seconds (queued for 2 seconds)
latest detached
Status Job ID Name Coverage
  Build
manual build:centos6-x86_64 #5776290
linux docker build cmake manual
passed build:debian10-iwyu #5776287
linux docker build cmake

00:02:43

manual build:fedora33-ninja #5776291
linux-3.17 linux docker build cmake manual
passed build:fedora33-sphinx #5776289
linux-3.17 linux docker build cmake

00:05:58

passed build:fedora33-tidy #5776288
linux-3.17 linux docker build cmake

00:06:53

manual build:macos-x86_64-makefiles #5776293
nonconcurrent xcode-12.4 shell macos cmake manual
manual build:macos-x86_64-ninja #5776292
cmake nonconcurrent xcode-12.4 shell macos manual
manual build:windows-vs2019-x64-ninja #5776294
nonconcurrent msvc-19.28-16.9 vs2019 shell windows cmake manual
 
  Test
created test:fedora33-ninja #5776295
x11 linux-3.17 linux docker cmake
created test:macos-x86_64-makefiles #5776297
nonconcurrent xcode-12.4 shell macos cmake
created test:macos-x86_64-ninja #5776296
nonconcurrent xcode-12.4 shell macos cmake
created test:windows-vs2019-x64-ninja #5776298
nonconcurrent msvc-19.28-16.9 vs2019 shell windows cmake
 
  Test Ext
created test:cuda10.2-nvidia #5776301
linux docker cuda-rt cmake
created test:debian10-ninja #5776299
linux-3.17 linux docker build cmake
created test:fedora33-makefiles #5776300
linux-3.17 linux docker build cmake
created test:fedora33-ninja-multi #5776302
linux-3.17 linux docker build cmake
created test:macos-x86_64-xcode #5776303
concurrent xcode-12.4 shell macos cmake
created test:windows-vs2019-x64 #5776304
concurrent msvc-19.28-16.9 vs2019 shell windows cmake
 
  External
passed cdash

passed ghostflow-check-master

passed ghostflow-check-release

passed ghostflow-stager

passed cdash

passed cdash

passed cdash

passed cdash

passed ghostflow-check-master

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager