CLEANUP: improvements to the alignment macros

CLEANUP: improvements to the alignment macros

- It is now possible to use the THREAD_ALIGN and THREAD_ALIGNED macros
  without a parameter. In this case, we automatically align on the cache
  line size.
- The cache line size is set to 64 by default to match the current code,
  but it can be overridden on the command line.
- This required moving the DEFVAL/DEFNULL/DEFZERO macros to compiler.h
  instead of tools-t.h, to avoid namespace pollution if we included
  tools-t.h from compiler.h.