[llvm-objcopy] Fix sparc target endianness

Summary: AFAIK, the "sparc" target is big endian and the target for 32-bit little-endian SPARC is denoted as "sparcel". This patch fixes the endianness of "sparc" target and adds "sparcel" target for 32-bit little-endian SPARC.

Reviewers: espindola, alexshap, rupprecht, jhenderson

Reviewed By: jhenderson

Subscribers: jyknight, emaste, arichardson, fedor.sergeev, jakehehrlich, MaskRay, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D63251

llvm-svn: 363336