Track protos + globals w/out initializers as undef too (not just helper funcs)

Also handle empty global variable lists -- and initialize
ShAddralign to 1 instead of 0, just in case. Previously
it would try to align by 0 when the variable list was empty.

This should help the crosstests pass with --elf.

BUG=none
R=kschimpf@google.com, stichnot@chromium.org

Review URL: https://codereview.chromium.org/899483002