[CMake][Release] Add stage2-package target (#89517)

This target will be used to generate the release binary package for
uploading to GitHub.

(cherry picked from commit a38f201)

Author: tstellar

clang/cmake/caches/Release.cmake

@@ -14,6 +14,7 @@ if (LLVM_RELEASE_ENABLE_PGO)
   set(CLANG_BOOTSTRAP_TARGETS
     generate-profdata
     stage2
+    stage2-package
     stage2-clang
     stage2-distribution
     stage2-install
@@ -57,6 +58,7 @@ set(LLVM_TARGETS_TO_BUILD Native CACHE STRING "")
 set(BOOTSTRAP_CLANG_ENABLE_BOOTSTRAP ON CACHE STRING "")
 set(BOOTSTRAP_CLANG_BOOTSTRAP_TARGETS
   clang
+  package
   check-all
   check-llvm
   check-clang CACHE STRING "")