Please see
https://lists.ubuntu.com/archives/ubuntu-devel/2021-January/041341.html https://wiki.ubuntu.com/ToolChain/LTO
Some builds only fail on AArch64, these are:
buildlog_ubuntu-hirsute-arm64.abiword_3.0.4~dfsg-2_BUILDING.txt.gz arm64 buildlog_ubuntu-hirsute-arm64.adabrowse_4.0.3-12_BUILDING.txt.gz arm64 buildlog_ubuntu-hirsute-arm64.adacontrol_1.21r6b-5_BUILDING.txt.gz arm64 buildlog_ubuntu-hirsute-arm64.armnn_19.11.1-1_BUILDING.txt.gz arm64 buildlog_ubuntu-hirsute-arm64.cctools_7.1.2-2ubuntu3_BUILDING.txt.gz arm64 buildlog_ubuntu-hirsute-arm64.csound_1:6.14.0~dfsg-6build1_BUILDING.txt.gz arm64 buildlog_ubuntu-hirsute-arm64.dh-ada-library_6.20_BUILDING.txt.gz arm64 buildlog_ubuntu-hirsute-arm64.dietlibc_0.34~cvs20160606-12_BUILDING.txt.gz arm64 buildlog_ubuntu-hirsute-arm64.entropybroker_2.9-3build2_BUILDING.txt.gz arm64 buildlog_ubuntu-hirsute-arm64.fpc_3.2.0+dfsg-8build2_BUILDING.txt.gz arm64 buildlog_ubuntu-hirsute-arm64.grcompiler_5.2-2.1_BUILDING.txt.gz arm64 buildlog_ubuntu-hirsute-arm64.haskell-hopenpgp-tools_0.23.1-1build2_BUILDING.txt.gz arm64 buildlog_ubuntu-hirsute-arm64.ignition-common_3.5.0+dfsg1-4_BUILDING.txt.gz arm64 buildlog_ubuntu-hirsute-arm64.lazarus_2.0.10+dfsg-4_BUILDING.txt.gz arm64 buildlog_ubuntu-hirsute-arm64.lepton-eda_1.9.13-1_BUILDING.txt.gz arm64 buildlog_ubuntu-hirsute-arm64.libcxx-serial_1.2.1-4_BUILDING.txt.gz arm64 buildlog_ubuntu-hirsute-arm64.minetest_5.3.0+repack-1_BUILDING.txt.gz arm64 buildlog_ubuntu-hirsute-arm64.ogre-1.12_1.12.5+dfsg1-1ubuntu1_BUILDING.txt.gz arm64 buildlog_ubuntu-hirsute-arm64.openmsx_16.0-1_BUILDING.txt.gz arm64 buildlog_ubuntu-hirsute-arm64.parsinsert_1.04-7ubuntu1_BUILDING.txt.gz arm64 buildlog_ubuntu-hirsute-arm64.prometheus-alertmanager_0.21.0+ds-2build1_BUILDING.txt.gz arm64 buildlog_ubuntu-hirsute-arm64.pyqt5_5.15.2+dfsg-1_BUILDING.txt.gz arm64 buildlog_ubuntu-hirsute-arm64.racon_1.4.13-2build1_BUILDING.txt.gz arm64 buildlog_ubuntu-hirsute-arm64.rampler_1.1.1-3_BUILDING.txt.gz arm64 buildlog_ubuntu-hirsute-arm64.ruby-http-parser.rb_0.6.0-5_BUILDING.txt.gz arm64 buildlog_ubuntu-hirsute-arm64.shasta_0.6.0-4build1_BUILDING.txt.gz arm64 buildlog_ubuntu-hirsute-arm64.snd_20.9-1_BUILDING.txt.gz arm64 buildlog_ubuntu-hirsute-arm64.sogo_4.3.2-1_BUILDING.txt.gz arm64 buildlog_ubuntu-hirsute-arm64.swiglpk_4.65.0-2build3_BUILDING.txt.gz arm64 buildlog_ubuntu-hirsute-arm64.synfig_1.2.2+dfsg-3build3_BUILDING.txt.gz arm64 buildlog_ubuntu-hirsute-arm64.synfigstudio_1.2.2-1build1_BUILDING.txt.gz arm64 buildlog_ubuntu-hirsute-arm64.tcc_0.9.27+git20200814.62c30a4a-1_BUILDING.txt.gz arm64 buildlog_ubuntu-hirsute-arm64.unar_1.10.1-2build9_BUILDING.txt.gz arm64 buildlog_ubuntu-hirsute-arm64.valgrind_1:3.16.1-1ubuntu1_BUILDING.txt.gz arm64 buildlog_ubuntu-hirsute-arm64.vulkan-tools_1.2.154.0+dfsg1-1_BUILDING.txt.gz arm64
Note that some of those like the Ada related ones are false positives, and I didn't look at the arm64 specific issues yet.
All builds were done using the GCC 10 branch.
Matthias