In an effort to minimize VM sizes, this change will cause runtime test
executables to be stripped, saving unstripped binaries under the ".dbg"
extension. The LDFLAGS and LIBS variables specified for each program are also
duplicated for the debug build.

This change reduces baseline memory requirements for various memory caches
under "low memory" conditions. If the function is_low_memory_machine() returns
true, then the following parameters are trimmed:

- the pagecache will use PAGECACHE_LOWMEM_CONTIGUOUS_PAGESIZE (default 128KB)
  as its objcache pagesize instead of PAGESIZE_2M
- the mcache high order is lowered to 11 (2KB), thus forcing PAGESIZE or
  larger allocations to be made directly from the backing heap - and thus not
  cached, nor available for situations that implement a malloc/free interface
- similiarly, allocations for lwIP are limited to a maximum size of 2KB

Given that there is limited queueing within the network stack, we can
reasonably predict that only up to virtqueue_entries(vn->rxq) rx buffers will
need to be cached - and similarly for tx handler completions. This adjusts the
objcache parent pagesizes to accommodate only these requirements, regardless
of whether the machine is in a 'low memory' configuration.

This modifies the mcache to allow using a malloc/free-style interface (where
the allocation size is not specified on a free()) when allocation sizes exceed
the largest objcache size. Such use would previously result in an error when
attempting to free such large allocations. To accomplish this, the mcache now
maintains a mapping of large allocation addresses to their corresponding
sizes. When a deallocate with an unspecified (-1ull) size occurs, a table
lookup/removal is made to check if the address corresponds to such a
"fallback" allocation and, if so, recover the allocation size.

The cost of using this fallback table is an insertion when making a
fallback (large) allocation and a table lookup/removal when deallocating a
fallback allocation of a known size, or on any deallocation (free) of an
unknown size. This should not impact the vast majority of mcache uses, for
which 1) the allocation size falls within the domain of the contained
objcaches and 2) the size parameter is valid on deallocation.