Set fill character other than zero

Mainly for more reliable testing.
Test that local memory is emptied
Define __PLATFORM_INTEL__
Use extension to initialize memory, if available.
Fix compilation error for unsupported-builtins test

error: event_t can't be used as kernel argument in OpenCL
Fix compiler warnings in check-empty-memory test.

Also fix incorrect underscore usage in member names.

Signed-off-by: Rami Ylimäki <rami.ylimaki@vincit.fi>
Add support for local and constant address space null pointers.

Signed-off-by: Rami Ylimäki <rami.ylimaki@vincit.fi>