[CMake][PGO] Add libunwind to list of stage1 runtimes (#78869)

This fixes the build since 8f90e69
which made libcxxabi use llvm's libunwind by default.

Fixes #78487

Author: tstellar

clang/cmake/caches/PGO.cmake

@@ -2,7 +2,7 @@ set(CMAKE_BUILD_TYPE RELEASE CACHE STRING "")
 set(CLANG_ENABLE_BOOTSTRAP ON CACHE BOOL "")
 
 set(LLVM_ENABLE_PROJECTS "clang;lld" CACHE STRING "")
-set(LLVM_ENABLE_RUNTIMES "compiler-rt;libcxx;libcxxabi" CACHE STRING "")
+set(LLVM_ENABLE_RUNTIMES "compiler-rt;libcxx;libcxxabi;libunwind" CACHE STRING "")
 
 set(LLVM_TARGETS_TO_BUILD Native CACHE STRING "")
 set(BOOTSTRAP_LLVM_BUILD_INSTRUMENTED ON CACHE BOOL "")