llvm-objdump: support dumping AUX records for weak externals

This is a support COFF feature.  Ensure that we can display the weak externals
auxiliary symbol.  It contains useful information (such as the default binding
and how to resolve the symbol).

This reapplies the previous patch with a modification which hopefully should fix
the endianness issues.  The variadic call would promote the ulittle32_t to a
uint32_t which would lose the byte-swapping behaviour desired.

llvm-svn: 270813