[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>
(cherry picked from commit 3af5c98)

llvm/utils/release/test-release.sh

@@ -532,9 +532,9 @@ function build_llvmCore() {
       BuildTarget="clang"
       InstallTarget="install-clang install-clang-resource-headers"
       # compiler-rt builtins is needed on AIX to have a functional Phase 1 clang.
-      if [ "$System" = "AIX" -o "$Phase" != "1" ]; then
+      if [ "$System" = "AIX" ]; then
         BuildTarget="$BuildTarget runtimes"
-        InstallTarget="$InstallTarget install-runtimes"
+        InstallTarget="$InstallTarget install-builtins"
       fi
     fi
     if [ "$Phase" -eq "3" ]; then