[Fuchsia] Don't use LLVM build for PGO data (#149788)

diff --git a/clang/cmake/caches/Fuchsia-stage2-instrumented.cmake b/clang/cmake/caches/Fuchsia-stage2-instrumented.cmake
index ecd478a..b328f3d 100644
--- a/clang/cmake/caches/Fuchsia-stage2-instrumented.cmake
+++ b/clang/cmake/caches/Fuchsia-stage2-instrumented.cmake
@@ -43,3 +43,6 @@
   ${EXTRA_ARGS}
   -C ${CMAKE_CURRENT_LIST_DIR}/Fuchsia-stage2.cmake
   CACHE STRING "")
+
+# Do not use LLVM build for generating PGO data.
+set(CLANG_PGO_TRAINING_USE_LLVM_BUILD OFF CACHE BOOL "")