None of the _mpd_shortadd() or _mpd_shortmul() functions read uninitialized
values. Previously zeroing was required since _mpd_real_size() was called
on the output array.

  for host compiler.

   require values set in CONFIG_SITE.

set cross_compiling = False for now.

use log10() to calculate the size of the output array. The current code
has been tested on x86/amd64 (and to a lesser extent on qemu-mips qemu-sparc)
and produces sufficiently large values for all inputs tested so far (coefficient
sizes of 10**18 - 1 are hard to test exhaustively).

The new code does not rely on the correctness of log10() and resizes
the output arrays if the allocated space is insufficient.

Patch by Marc Abramowitz.

  AC_PATH_PROG and AC_CHECK_PROGS for the target tools.

  global host_platform instead.

the Ctrl-C signal handler on Windows

the Ctrl-C signal handler on Windows

Patch by Serhiy Storchaka.

Patch by Serhiy Storchaka.

Patch by Jakub Wilk.