PNaCl: ExpandTls: Use C++11 range-based "for" loops

Also use use_empty() rather than hasNUsesOrMore(1) since the former is
clearer.

BUG=https://bugs.chromium.org/p/nativeclient/issues/detail?id=4351
TEST=test/Transforms/NaCl/expand-tls*.ll
R=smklein@chromium.org

Review URL: https://codereview.chromium.org/1759263003 .
1 file changed