Fix llvm-nm to print the full 64-bit address for symbols in 64-bit object files.

The implementation might be better to have a method is64Bit() in the class
SymbolicFile instead of having the static routine isSymbolList64Bit() in
llvm-nm.cpp .  But this is very much in the sprit of isObject() and
getNMTypeChar() in llvm-nm.cpp that has a series of if else statements
based on the specific class of the SymbolicFile.  I can update this if
folks would like.

Also the tests were updated to be explicit about checking the address for
64-bits or 32-bits from object files.