[macho] Allow CPUSubtype to contribute to architecture identification

[dsanders]

Summary

Sometimes the CPUSubtype determines the Triple::ArchType that must be used.
Add the subtype to the API's to allow targets that need this to correctly
identify the contents of the binary.

[pete]

LGTM

llvm/include/llvm/Object/MachO.h

public:
 
   StringRef getStringTableData() const;
   bool is64Bit() const;
   void ReadULEB128s(uint64_t Index, SmallVectorImpl<uint64_t> &Out) const;
 
   static StringRef guessLibraryShortName(StringRef Name, bool &isFramework,
                                          StringRef &Suffix);
 
-  static Triple::ArchType getArch(uint32_t CPUType);
+  static Triple::ArchType getArch(uint32_t CPUType, uint32_t CPUSubType);
   static Triple getArchTriple(uint32_t CPUType, uint32_t CPUSubType,
                               const char **McpuDefault = nullptr,
                               const char **ArchFlag = nullptr);
   static bool isValidArch(StringRef ArchFlag);
   static ArrayRef<StringRef> getValidArchs();
   static Triple getHostArch();
 
   bool isRelocatableObject() const override;

llvm/lib/Object/MachOObjectFile.cpp

static StringRef parseSegmentOrSectionName(const char *P) {
   // Not null terminated, so this is a 16 char string.
   return StringRef(P, 16);
 }
 
 static unsigned getCPUType(const MachOObjectFile &O) {
   return O.getHeader().cputype;
 }
 
+static unsigned getCPUSubType(const MachOObjectFile &O) {
+  return O.getHeader().cpusubtype;
+}
+
 static uint32_t
 getPlainRelocationAddress(const MachO::any_relocation_info &RE) {
   return RE.r_word0;
 }
 
 static unsigned
 getScatteredRelocationAddress(const MachO::any_relocation_info &RE) {
   return RE.r_word0 & 0xffffff;
case MachO::CPU_TYPE_ARM64:
     return "Mach-O arm64";
   case MachO::CPU_TYPE_POWERPC64:
     return "Mach-O 64-bit ppc64";
   default:
     return "Mach-O 64-bit unknown";
   }
 }
 
-Triple::ArchType MachOObjectFile::getArch(uint32_t CPUType) {
+Triple::ArchType MachOObjectFile::getArch(uint32_t CPUType, uint32_t CPUSubType) {
   switch (CPUType) {
   case MachO::CPU_TYPE_I386:
     return Triple::x86;
   case MachO::CPU_TYPE_X86_64:
     return Triple::x86_64;
   case MachO::CPU_TYPE_ARM:
     return Triple::arm;
   case MachO::CPU_TYPE_ARM64:
static const std::array<StringRef, 17> validArchs = {{
       "armv6",  "armv6m", "armv7",    "armv7em", "armv7k", "armv7m",
       "armv7s", "arm64",  "arm64_32", "ppc",     "ppc64",
   }};
 
   return validArchs;
 }
 
 Triple::ArchType MachOObjectFile::getArch() const {
-  return getArch(getCPUType(*this));
+  return getArch(getCPUType(*this), getCPUSubType(*this));
 }
 
 Triple MachOObjectFile::getArchTriple(const char **McpuDefault) const {
   return getArchTriple(Header.cputype, Header.cpusubtype, McpuDefault);
 }
 
 relocation_iterator MachOObjectFile::section_rel_begin(unsigned Index) const {
   DataRefImpl DRI;