For the POSIX regexp interface, move local declaration to beginning
of block to avoid requiring C99. Also switch to alloc() from bare
malloc() so that MONITOR_HEAP won't log a free which doesn't match
up to any allocation. This results in a change in behavior: if
the allocation fails, nethack will panic rather than report an
option parsing error. In practice there will be no difference
because nethack is not going to run out of dynamic memory during
initial options processing.
cf74f1cfd8