Normalize arena_palloc(), chunk_alloc_mmap_slow(), and
chunk_recycle_dss() to use the same algorithm for trimming
over-allocation.
Add the ALIGNMENT_ADDR2BASE(), ALIGNMENT_ADDR2OFFSET(), and
ALIGNMENT_CEILING() macros, and use them where appropriate.
Remove the run_size_p parameter from sa2u().
Fix a potential deadlock in chunk_recycle_dss() that was introduced by
eae269036c9f702d9fa9be497a1a2aa1be13a29e (Add alignment support to
chunk_alloc()).
5ff709c264