[lld/mac] On Apple systems, call CC_SHA256 from libSystem

It's in libSystem, so it doesn't bring in any new deps, and it's
currently much faster than LLVM's current SHA256 implementation.

Makes linking (arm64) Chromium Framework with ld64.lld 17% faster.
See also PR56121.

No behavior change.

Differential Revision: https://reviews.llvm.org/D128290

lld/MachO/SyntheticSections.cpp

@@ -23,10 +23,14 @@
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/LEB128.h"
 #include "llvm/Support/Path.h"
-#include "llvm/Support/SHA256.h"
 
 #if defined(__APPLE__)
 #include <sys/mman.h>
+
+#define COMMON_DIGEST_FOR_OPENSSL
+#include <CommonCrypto/CommonDigest.h>
+#else
+#include "llvm/Support/SHA256.h"
 #endif
 
 #ifdef LLVM_HAVE_LIBXAR
@@ -45,10 +49,16 @@ using namespace lld::macho;
 
 // Reads `len` bytes at data and writes the 32-byte SHA256 checksum to `output`.
 static void sha256(const uint8_t *data, size_t len, uint8_t *output) {
+#if defined(__APPLE__)
+  // FIXME: Make LLVM's SHA256 faster and use it unconditionally. See PR56121
+  // for some notes on this.
+  CC_SHA256(data, len, output);
+#else
   ArrayRef<uint8_t> block(data, len);
   std::array<uint8_t, 32> hash = SHA256::hash(block);
   assert(hash.size() == CodeSignatureSection::hashSize);
   memcpy(output, hash.data(), hash.size());
+#endif
 }
 
 InStruct macho::in;