[Release] Install compiler-rt builtins during Phase 1 on AIX (#81485)

The current test-release.sh script does not install the necessary
compiler-rt builtin's during Phase 1 on AIX, resulting on a
non-functional Phase 1 clang. Futhermore, the installation is also
necessary for Phase 2 on AIX.

Co-authored-by: Alison Zhang <alisonzhang@ibm.com>