[Tests] Output of od can be lower or upper case (llvm-objcopy/yaml2obj).

The command `od -t x` is used to dump data in hex format.
The LIT tests assumes that the hex characters are in lowercase.
However, there are also platforms which use uppercase letter.

To solve this issue the tests are updated to use the new
`--ignore-case` option of FileCheck.

Reviewers: Bigcheese, jakehehrlich, rupprecht, espindola, alexshap, jhenderson

Differential Revision: https://reviews.llvm.org/D68693

llvm-svn: 374547