Also changes the szbuild.py script to add -fdata-sections, and entirely removes the -disable-globals option.
The global initializer emission basically copies what llc does, based on 3 properties of the global: constant vs non-constant, internal vs external, and full zero-initializer vs non-trivial initializer.
BUG= none
R=jvoung@chromium.org, kschimpf@google.com
Review URL: https://codereview.chromium.org/631383003
