[llvm-objdump] Change symbol name/PLT decoding errors to warnings
If the referenced symbol of a J[U]MP_SLOT is invalid (e.g. symbol index 0), llvm-objdump -d will bail out:
error: 'a': st_name (0x326600) is past the end of the string table of size 0x7
where 0x326600 is the st_name field of the first entry past the end of .symtab
Change it to a warning to continue dumping.
X86/plt.test uses a prebuilt executable, so I pick ELF/AArch64/plt.test
which has a YAML input and can be easily modified.
Reviewed By: jhenderson
Differential Revision: https://reviews.llvm.org/D85623