Sink DwarfUnit::CURanges into DwarfCompileUnit
Emit OpenCL local global variables without zeorinitializer

Local variables are not initialized, and every target has
been (incorrectly) ignoring the unnecessary request for
zero initialization.
This patch reverts r220496 which issues warning on comparing
parameters with nonnull attribute when comparison is always
true/false. Patch causes false positive when parameter is
modified in the function.