[builtins] Fix CPU feature detection for Zircon (#76276)

This is a follow up to #75635 which broke the build on Fuchsia. We don't
support ifunc on Fuchsia so we shouldn't define __init_cpu_features. For
__init_cpu_features_resolver we have to use _zx_system_get_features as a
Zircon native solution.

compiler-rt/lib/builtins/cpu_model/aarch64.c

@@ -133,7 +133,6 @@ struct {
 #include "aarch64/fmv/mrs.inc"
 #include "aarch64/fmv/freebsd.inc"
 #elif defined(__Fuchsia__)
-#include "aarch64/fmv/mrs.inc"
 #include "aarch64/fmv/fuchsia.inc"
 #elif defined(__ANDROID__)
 #include "aarch64/fmv/mrs.inc"

compiler-rt/lib/builtins/cpu_model/aarch64/fmv/fuchsia.inc

@@ -1,22 +1,51 @@
-void __init_cpu_features_resolver(unsigned long hwcap,
-                                  const __ifunc_arg_t *arg) {
+#include <zircon/features.h>
+#include <zircon/syscalls.h>
+
+void __init_cpu_features_resolver() {
   if (__aarch64_cpu_features.features)
     return;
 
-  __init_cpu_features_constructor(hwcap, arg);
-}
-
-void CONSTRUCTOR_ATTRIBUTE __init_cpu_features(void) {
-  // CPU features already initialized.
-  if (__aarch64_cpu_features.features)
+    // This ensures the vDSO is a direct link-time dependency of anything that
+    // needs this initializer code.
+#pragma comment(lib, "zircon")
+  uint32_t features;
+  zx_status_t status = _zx_system_get_features(ZX_FEATURE_KIND_CPU, &features);
+  if (status != ZX_OK)
     return;
 
-  unsigned long hwcap = getauxval(AT_HWCAP);
-  unsigned long hwcap2 = getauxval(AT_HWCAP2);
+#define setCPUFeature(cpu_feature)                                             \
+  __aarch64_cpu_features.features |= 1ULL << cpu_feature
+
+  if (features & ZX_ARM64_FEATURE_ISA_FP)
+    setCPUFeature(FEAT_FP);
+  if (features & ZX_ARM64_FEATURE_ISA_ASIMD)
+    setCPUFeature(FEAT_SIMD);
+  if (features & ZX_ARM64_FEATURE_ISA_AES)
+    setCPUFeature(FEAT_AES);
+  if (features & ZX_ARM64_FEATURE_ISA_PMULL)
+    setCPUFeature(FEAT_PMULL);
+  if (features & ZX_ARM64_FEATURE_ISA_SHA1)
+    setCPUFeature(FEAT_SHA1);
+  if (features & ZX_ARM64_FEATURE_ISA_SHA256)
+    setCPUFeature(FEAT_SHA2);
+  if (features & ZX_ARM64_FEATURE_ISA_CRC32)
+    setCPUFeature(FEAT_CRC);
+  if (features & ZX_ARM64_FEATURE_ISA_RDM)
+    setCPUFeature(FEAT_RDM);
+  if (features & ZX_ARM64_FEATURE_ISA_SHA3)
+    setCPUFeature(FEAT_SHA3);
+  if (features & ZX_ARM64_FEATURE_ISA_SM4)
+    setCPUFeature(FEAT_SM4);
+  if (features & ZX_ARM64_FEATURE_ISA_DP)
+    setCPUFeature(FEAT_DOTPROD);
+  if (features & ZX_ARM64_FEATURE_ISA_FHM)
+    setCPUFeature(FEAT_FP16FML);
+  if (features & ZX_ARM64_FEATURE_ISA_SHA512)
+    setCPUFeature(FEAT_SHA3);
+  if (features & ZX_ARM64_FEATURE_ISA_I8MM)
+    setCPUFeature(FEAT_I8MM);
+  if (features & ZX_ARM64_FEATURE_ISA_SVE)
+    setCPUFeature(FEAT_SVE);
 
-  __ifunc_arg_t arg;
-  arg._size = sizeof(__ifunc_arg_t);
-  arg._hwcap = hwcap;
-  arg._hwcap2 = hwcap2;
-  __init_cpu_features_constructor(hwcap | _IFUNC_ARG_HWCAP, &arg);
+  setCPUFeature(FEAT_INIT);
 }