[macho2yaml][test] Specify the object file's endianness. NFC.

This patch is intended to fix testing failure on big endian machine.

Failed testing: http://lab.llvm.org:8011/builders/clang-ppc64be-linux/builds/52450

Author: higuoxing

llvm/test/tools/obj2yaml/MachO/debug-aranges.yaml

@@ -30,6 +30,7 @@
 # ARANGES-NEXT:           Length:          0x0000000000005678
 
 --- !mach-o
+IsLittleEndian: true
 FileHeader:
   magic:      0xFEEDFACF
   cputype:    0x01000007