[CUDA] Add CUDA fatbinary magic

[jhuber6]

Summary

Nvidia uses fatbinaries to bundle all of their device code. This patch
adds the magic number "0x50ed55ba" used in their propeitary format to
the list of magic identifies. This is technically undocumented and could
unlikely be changed by Nvidia in the future.

[tra]

LGTM with a nit.

llvm/lib/BinaryFormat/Magic.cpp

196–197

I'd move it up to case 0x50:

[jhuber6]

Addressing nit

llvm/include/llvm/BinaryFormat/Magic.h

enum Impl {
     coff_import_library, ///< COFF import library
     pecoff_executable,   ///< PECOFF executable file
     windows_resource,    ///< Windows compiled resource file (.res)
     xcoff_object_32,     ///< 32-bit XCOFF object file
     xcoff_object_64,     ///< 64-bit XCOFF object file
     wasm_object,         ///< WebAssembly Object file
     pdb,                 ///< Windows PDB debug info file
     tapi_file,           ///< Text-based Dynamic Library Stub file
+    cuda_fatbinary,      ///< CUDA Fatbinary object file
   };
 
   bool is_object() const { return V != unknown; }
 
   file_magic() = default;
   file_magic(Impl V) : V(V) {}
   operator Impl() const { return V; }
 

llvm/lib/BinaryFormat/Magic.cpp

case 0xCF: {
     }
     break;
   }
   case 0xF0: // PowerPC Windows
   case 0x83: // Alpha 32-bit
   case 0x84: // Alpha 64-bit
   case 0x66: // MPS R4000 Windows
   case 0x50: // mc68K
+    if (startswith(Magic, "\x50\xed\x55\xba"))
+      return file_magic::cuda_fatbinary;
+    LLVM_FALLTHROUGH;
+
   case 0x4c: // 80386 Windows
   case 0xc4: // ARMNT Windows
     if (Magic[1] == 0x01)
       return file_magic::coff_object;
     LLVM_FALLTHROUGH;
 
   case 0x90: // PA-RISC Windows
   case 0x68: // mc68K Windows
     if (Magic[1] == 0x02)
       return file_magic::coff_object;
     break;
 
   case 'M': // Possible MS-DOS stub on Windows PE file, MSF/PDB file or a
             // Minidump file.

llvm/lib/Object/Binary.cpp

Expected<std::unique_ptr<Binary>> object::createBinary(MemoryBufferRef Buffer,
   case file_magic::macho_universal_binary:
     return MachOUniversalBinary::create(Buffer);
   case file_magic::windows_resource:
     return WindowsResource::createWindowsResource(Buffer);
   case file_magic::pdb:
     // PDB does not support the Binary interface.
     return errorCodeToError(object_error::invalid_file_type);
   case file_magic::unknown:
+  case file_magic::cuda_fatbinary:
   case file_magic::coff_cl_gl_object:
     // Unrecognized object file format.
     return errorCodeToError(object_error::invalid_file_type);
   case file_magic::minidump:
     return MinidumpFile::create(Buffer);
   case file_magic::tapi_file:
     return TapiUniversal::create(Buffer);
   }

llvm/lib/Object/ObjectFile.cpp

ObjectFile::createObjectFile(MemoryBufferRef Object, file_magic Type,
   case file_magic::bitcode:
   case file_magic::coff_cl_gl_object:
   case file_magic::archive:
   case file_magic::macho_universal_binary:
   case file_magic::windows_resource:
   case file_magic::pdb:
   case file_magic::minidump:
   case file_magic::goff_object:
+  case file_magic::cuda_fatbinary:
     return errorCodeToError(object_error::invalid_file_type);
   case file_magic::tapi_file:
     return errorCodeToError(object_error::invalid_file_type);
   case file_magic::elf:
   case file_magic::elf_relocatable:
   case file_magic::elf_executable:
   case file_magic::elf_shared_object:
   case file_magic::elf_core: