[ELF] Correctly set the nvptx triple from makeTriple() (#76970)

Summary:
The ELFObject file should be able to handle `nvptx` objects but we
currently list them as unknown. This patch should now make it return
`nvptx64--` correctly.

Author: jhuber6

llvm/include/llvm/Object/ELFObjectFile.h

@@ -1349,6 +1349,13 @@ template <class ELFT> Triple::ArchType ELFObjectFile<ELFT>::getArch() const {
     return Triple::UnknownArch;
   }
 
+  case ELF::EM_CUDA: {
+    if (EF.getHeader().e_ident[ELF::EI_CLASS] == ELF::ELFCLASS32)
+      return Triple::nvptx;
+    else
+      return Triple::nvptx64;
+  }
+
   case ELF::EM_BPF:
     return IsLittleEndian ? Triple::bpfel : Triple::bpfeb;