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 Name Job ID Coverage
  Build
manual build:centos6-x86_64 #5776290
cmake build docker linux manual
passed build:debian10-iwyu #5776287
cmake build docker linux

00:02:43

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

00:05:58

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

00:06:53

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