[yaml2obj][tests] Replace 8-byte `od` conversion with 1-byte conversion

Summary:
`od` on AIX does not seem to implement 8-byte integer conversions. Work
around this by using 1-byte conversions, which can be used in this case
since the value is byte-order insensitive.

Reviewers: grimar, daltenty, xingxue, jasonliu, MaskRay

Reviewed By: grimar, MaskRay

Subscribers: MaskRay, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D65671

llvm-svn: 367760