Merge commit 'c3da16b09451' from llvm.org/release/19.x into stable/20240723

Author: git apple-llvm automerger

libunwind/src/cet_unwind.h

@@ -39,9 +39,13 @@
 // need to guard any use of GCS instructions with __chkfeat though, as GCS may
 // not be enabled.
 #if defined(_LIBUNWIND_TARGET_AARCH64) && defined(__ARM_FEATURE_GCS_DEFAULT)
-#define _LIBUNWIND_USE_GCS 1
 #include <arm_acle.h>
 
+// We can only use GCS if arm_acle.h defines the GCS intrinsics.
+#ifdef _CHKFEAT_GCS
+#define _LIBUNWIND_USE_GCS 1
+#endif
+
 #define _LIBUNWIND_POP_CET_SSP(x)                                              \
   do {                                                                         \
     if (__chkfeat(_CHKFEAT_GCS)) {                                             \