[gcs] Support Guarded Control Stacks (#100)

Add support for Guarded Control Stacks in all components, and allow allocating
new stacks in the simulator.
diff --git a/src/cpu-features.h b/src/cpu-features.h
index 97eb661..1a041f6 100644
--- a/src/cpu-features.h
+++ b/src/cpu-features.h
@@ -201,7 +201,8 @@
   /* Extended BFloat16 instructions                                         */ \
   V(kEBF16,               "EBF16",                  "ebf16")                   \
   V(kSVE_EBF16,           "EBF16 (SVE)",            "sveebf16")                \
-  V(kCSSC,                "CSSC",                   "cssc")
+  V(kCSSC,                "CSSC",                   "cssc")                    \
+  V(kGCS,                 "GCS",                    "gcs")
 // clang-format on