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

[thakis]

Summary

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 Chromium Framework with ld64.lld 17% faster. See also PR56121.

No behavior change.

[oontvoo]

Nice!!

[int3]

17%, wow

lld/MachO/SyntheticSections.cpp

 
 #include "lld/Common/CommonLinkerContext.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/Config/llvm-config.h"
 #include "llvm/Support/EndianStream.h"
 #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
 #include <fcntl.h>
 extern "C" {
 #include <xar/xar.h>
 }
 #endif
 
 using namespace llvm;
 using namespace llvm::MachO;
 using namespace llvm::support;
 using namespace llvm::support::endian;
 using namespace lld;
 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;
 std::vector<SyntheticSection *> macho::syntheticSections;
 
 SyntheticSection::SyntheticSection(const char *segname, const char *name)
     : OutputSection(SyntheticKind, name) {
   std::tie(this->segname, this->name) = maybeRenameSection({segname, name});