[llvm-install-name-tool] Merge install-name options

This diff merges all options for llvm-install-name-tool under a single
function processLoadCommands. Also adds another test case for -add_rpath
option.

Test plan: make check-all

Reviewed by: jhenderson, alexshap, smeenai, Ktwu

Differential Revision: https://reviews.llvm.org/D82812