internal/cpu: add ARM64.HasSHA3

For golang#69536

Change-Id: If237226ba03e282443b4fc90484968c903198cb1

Author: FiloSottile

src/internal/cpu/cpu.go

@@ -70,6 +70,7 @@ var ARM64 struct {
 	HasSHA1    bool
 	HasSHA2    bool
 	HasSHA512  bool
+	HasSHA3    bool
 	HasCRC32   bool
 	HasATOMICS bool
 	HasCPUID   bool

src/internal/cpu/cpu_arm64_darwin.go

@@ -9,15 +9,21 @@ package cpu
 import _ "unsafe" // for linkname
 
 func osInit() {
+	// macOS 12 moved these to the hw.optional.arm tree, but as of Go 1.24 we
+	// still support macOS 11. See [Determine Encryption Capabilities].
+	//
+	// [Determine Encryption Capabilities]: https://developer.apple.com/documentation/kernel/1387446-sysctlbyname/determining_instruction_set_characteristics#3918855
 	ARM64.HasATOMICS = sysctlEnabled([]byte("hw.optional.armv8_1_atomics\x00"))
 	ARM64.HasCRC32 = sysctlEnabled([]byte("hw.optional.armv8_crc32\x00"))
 	ARM64.HasSHA512 = sysctlEnabled([]byte("hw.optional.armv8_2_sha512\x00"))
+	ARM64.HasSHA3 = sysctlEnabled([]byte("hw.optional.armv8_2_sha3\x00"))
+
 	ARM64.HasDIT = sysctlEnabled([]byte("hw.optional.arm.FEAT_DIT\x00"))
 
-	// There are no hw.optional sysctl values for the below features on Mac OS 11.0
-	// to detect their supported state dynamically. Assume the CPU features that
-	// Apple Silicon M1 supports to be available as a minimal set of features
-	// to all Go programs running on darwin/arm64.
+	// There are no hw.optional sysctl values for the below features on macOS 11
+	// to detect their supported state dynamically (although they are available
+	// in the hw.optional.arm tree on macOS 12). Assume the CPU features that
+	// Apple Silicon M1 supports to be available on all future iterations.
 	ARM64.HasAES = true
 	ARM64.HasPMULL = true
 	ARM64.HasSHA1 = true