Fix issues with aarch64 GCC

[Bo98]

1.1.1 candidate release

aarch64 fixes:

• Fix portability of aarch64 GCC on Ubuntu runners by always enabling multiarch rather than checking the host. This wasn't an issue on x86_64 since the host there was Debian whereas for aarch64 we're using CentOS here.
  • Note: multiarch is just a search directory thing - the build is still only a single architecture
• Build libgcc with branch protection so that we can build glibc with branch protection

Misc fixes while we're here:

• Fix some code scanning flags
• Combine release steps to allow immutable releases
• Exclude bot spam from release notes