tools/memory-model: Hardware checking for check{,all}litmus.sh

This commit makes checklitmus.sh and checkalllitmus.sh check to see
if a hardware verification was specified (via the --hw command-line
argument, which sets the LKMM_HW_MAP_FILE environment variable).
If so, the C-language litmus test is converted to the specified type
of assembly-language litmus test and herd is run on it.  Hardware is
permitted to be stronger than LKMM requires, so "Always" and "Never"
verifications of "Sometimes" C-language litmus tests are forgiven.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>