kernel: add 'void * ref' to all GC mark functions #5172

Job	Run time
Cross compiler for s390x	14m 8s
Test in OpenBSD	11m 33s
testinstall - - ubuntu-latest	4m 17s
teststandard - - ubuntu-latest	14m 29s
testmanuals - - ubuntu-latest	5m 40s
testexpect testmockpkg testspecial test-compile testlibgap testkernel testworkspace - - ubuntu-latest	6m 59s
testpackages testinstall-loadall - - ubuntu-latest	14m 27s
makemanuals testmakeinstall - CONFIGFLAGS="--prefix=/tmp/gapprefix" NO_COVERAGE=1 - ubuntu-latest	5m 30s
teststandard - ABI=32 CONFIGFLAGS="" - ubuntu-20.04	14m 19s
testinstall - HPCGAP=yes ABI=64 - ubuntu-latest	6m 50s
testmockpkg testinstall - BOOTSTRAP_MINIMAL=yes - macos-latest	5m 37s
testbugfix - CONFIGFLAGS="--enable-memory-checking" - ubuntu-latest	14m 19s
testbuildsys testmockpkg testinstall - NO_COVERAGE=1 ABI=64 BUILDDIR=out-of-tree CONFIGFLAGS="--enable-valgrind" - ubuntu-latest	4m 5s
testbuildsys testmockpkg testinstall - NO_COVERAGE=1 ABI=32 BUILDDIR=out-of-tree CONFIGFLAGS="" - ubuntu-20.04	3m 21s
testinstall - JULIA=yes CONFIGFLAGS="--enable-debug --disable-Werror" - ubuntu-20.04	1m 8s
testmockpkg testinstall - - windows-2019	14m 10s
Send Slack notification on status change	1s
	2h 20m 53s

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