[test/Object][llvm-objdump] - llvm-objdump: don't abort() when the e_phoff field is invalid and refine testing.
llvm-objdump currently calls report_fatal_error() when the e_phoff field is invalid.
This is tested by elf-invalid-phdr.test which has the following issues:
- It uses a precompiled object.
- it could be a part of invalid.test.
- It tests the Object lib, but we have no separate test for llvm-objdump.
This patch addresses issues mentioned.
Differential revision: https://reviews.llvm.org/D83559