Only use MULTIARCH_PATH if it is defined.

This fixes the build. Should probably be pulled up to pcc-1.1 if correct
new date 20141211
AC_C_BIGENDIAN() only takes three arguments according to GNU documentation

(makes no change in configure)
new date 20141213
there are no more arguments when lac == 1

fixes bug pointed out by Stephen Turner on pcc-list
new date 20141217
AC_HELP_STRING() is obsolete, use AS_HELP_STRING() instead
regenerate after update to autoconf 2.69
install the driver as p++ also

while here, rewrite the installation to use a loop (DRIVERS) rather
than a straight list
latest config.guess and config.sub from gnu.org

this should help with a problem not recognising linux with musl,
noted by stephen Turner on pcc-list
add back m16c (not in upstream)
add back Nova (not in upstream)
don't use return <void expression>; in a void function. Visual C++
complains about it, noted by Antoine Leca on pcc-list

Shame because its a nice construct, but I can't find anything in C99
that does allow this. 6.8.6.4 says that a return statement with an
expression shall not appear in a function whose return type is void,
and no concession is given for a void expression..
use inc/amd64.h for generic inclusions

from Antoine Leca, on pcc-list
allow --with-libdir=<dir> to override the use of /usr/lib again

from Antoine Leca, on pcc-list
re-enable -idirafter

from Antoine Leca on pcc-list
add arm and amd64 for minix
minix also wants floating point definitions
from Antoine Leca, on pcc-list
update minix support for new driver
from Antoine Leca, on pcc-list
do not use GNU extension case statement, be kind to compilers other
than GNU

from Antoine Leca, on pcc-list