[yaml2obj] - Allow using an arbitrary value for OSABI.

There was no way to set an unsupported or unknown OS ABI.
With this patch it is possible to use any numeric value.

Differential revision: https://reviews.llvm.org/D71765

lib/ObjectYAML/ELFYAML.cpp

@@ -275,6 +275,7 @@ void ScalarEnumerationTraits<ELFYAML::ELF_ELFOSABI>::enumeration(
   ECase(ELFOSABI_C6000_LINUX);
   ECase(ELFOSABI_STANDALONE);
 #undef ECase
+  IO.enumFallback<Hex8>(Value);
 }
 
 void ScalarBitSetTraits<ELFYAML::ELF_EF>::bitset(IO &IO,

test/tools/yaml2obj/ELF/header-osabi.yaml

@@ -325,3 +325,16 @@ FileHeader:
   Type:    ET_REL
   Machine: EM_X86_64
   OSABI:   ELFOSABI_STANDALONE
+
+## Test we can use an arbitrary number for OSABI.
+# RUN: yaml2obj %s --docnum=27 -o %t.number
+# RUN: llvm-readobj --file-headers %t.number | FileCheck %s --check-prefix=OSABI-NUMBER
+# OSABI-NUMBER: OS/ABI: 0xFE
+
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS64
+  Data:    ELFDATA2LSB
+  Type:    ET_REL
+  Machine: EM_X86_64
+  OSABI:   0xFE