GlobalOpt only process non constant local GVs while optimizing global vars.

If non constant local GV named A is used by a constant local GV named B (e.g. llvm.dbg.variable) and B is not used by anyone else then eliminate A as well as B.

In other words, debug info should not interfere in removal of unused GV.
--This life, and those below, will be ignored--

M    test/Transforms/GlobalOpt/2009-03-03-dbg.ll
M    lib/Transforms/IPO/GlobalOpt.cpp

llvm-svn: 66167