When both little-endian and big-endian are tested, or both 32-bit and 64-bit are tested, use a template like the following with `-D BITS=32 -D ENCODE=LSB`
```
--- !ELF
FileHeader:
Class: ELFCLASS[[BITS]]
Data: ELFDATA2[[ENCODE]]
Type: ET_DYN
Machine: EM_X86_64
```
Reviewed By: grimar, jhenderson
Differential Revision: https://reviews.llvm.org/D73828
