Use ELFOSABI_NONE. This matches both bfd ld and gold.

llvm-svn: 244033
diff --git a/lld/ELF/Writer.cpp b/lld/ELF/Writer.cpp
index 0f6adc9..91cb16e 100644
--- a/lld/ELF/Writer.cpp
+++ b/lld/ELF/Writer.cpp
@@ -123,7 +123,7 @@
   EHdr->e_ident[EI_CLASS] = ELFCLASS64;
   EHdr->e_ident[EI_DATA] = ELFDATA2LSB;
   EHdr->e_ident[EI_VERSION] = EV_CURRENT;
-  EHdr->e_ident[EI_OSABI] = ELFOSABI_GNU;
+  EHdr->e_ident[EI_OSABI] = ELFOSABI_NONE;
 
   EHdr->e_type = ET_EXEC;
   EHdr->e_machine = EM_X86_64;