General clean up of Mach-O error handling in llvm-objdump.

To get a good error message for all files that could contain Mach-O
files the code in llvm-objdump needs to use the archive member name
and name of the architecture of a slice of a universal file in those cases
where the error come from a Mach-O file in an archive or a universal file.

Most of this is fixed by moving the call to checkSymbolTable() into
ProcessMachO() and calling it when the operation needs the symbol
table.  And then calling the form of report_error() that has the
ArchiveName and ArchitectureName arguments.  One other place
needed to call this form of report_error() also with these arguments.

Also changed the code in MachODump.cpp to not use report_fatal_error()
and use report_error() instead to make the code smaller and cleaner.  All
cases of this are for errors with the symbol table which should now never
be tripped since checkSymbolTable() should be called first to get a good
error message in these cases.

llvm-svn: 287050