[llvm] [clang] [Github] Use building LLVM as perf-training for CI container (PR #80713)

[Tom Stellard via cfe-commits]

================
@@ -0,0 +1,13 @@
+diff --git a/clang/cmake/caches/BOLT-PGO.cmake b/clang/cmake/caches/BOLT-PGO.cmake
+index 1a04ca9a74e5..d092820e4115 100644
+--- a/clang/cmake/caches/BOLT-PGO.cmake
++++ b/clang/cmake/caches/BOLT-PGO.cmake
+@@ -4,6 +4,8 @@ set(CLANG_BOOTSTRAP_TARGETS
+   stage2-clang-bolt
+   stage2-distribution
+   stage2-install-distribution
++  clang
++  lld
----------------
tstellar wrote:

Do you need this because of the way you have split the stages?  If you were to to just run `ninja stage2-clang-bolt` from the start would it still be building a lot of unnecessary targets prior to generating the profile data?  I'm mainly wondering if this is a change that would benefit everyone using the BOLT-PGO cache.

https://github.com/llvm/llvm-project/pull/80713