[LLD][ELF] - Remove file-class.a binary from inputs and improve the test case.

file-class.a was used to diagnose the "corrupted ELF file: invalid file class"
error when the object was fetched from the archive.

file-class.a contained an object of 16 bytes size. I replaced it with
an echo call (because it is impossible to use yaml2obj for that, and I am
not sure it is worth to support), and also increased its size to 18 bytes.
That allowed to also test a case when such object is a regular input and not an
archive member (we have a bit different logic for these cases).

llvm-svn: 358985