FTBFS on hurd

starting in 0.2.3.11, tor fails to build from source on the hurd.

This might also be a change in environment rather than a change in tor that causes it to fail now.

make[4]: Entering directory `/build/buildd-tor_0.2.3.12-alpha-1-hurd-i386-9yxbax/tor-0.2.3.12-alpha/src/common'
gcc -DHAVE_CONFIG_H -I. -I../..   -I../../src/common     -fPIE  -fstack-protector --param ssp-buffer-size=4  -D_FORTIFY_SOURCE=2  -Wformat -Wformat-security -Werror=format-security  -O2 -Wall -fno-strict-aliasing -MT address.o -MD -MP -MF .deps/address.Tpo -c -o address.o address.c
mv -f .deps/address.Tpo .deps/address.Po
gcc -DHAVE_CONFIG_H -I. -I../..   -I../../src/common     -fPIE  -fstack-protector --param ssp-buffer-size=4  -D_FORTIFY_SOURCE=2  -Wformat -Wformat-security -Werror=format-security  -O2 -Wall -fno-strict-aliasing -MT compat.o -MD -MP -MF .deps/compat.Tpo -c -o compat.o compat.c
compat.c: In function 'make_path_absolute':
compat.c:1641:13: error: 'PATH_MAX' undeclared (first use in this function)
compat.c:1641:13: note: each undeclared identifier is reported only once for each function it appears in
compat.c:1641:8: warning: unused variable 'path' [-Wunused-variable]
make[4]: *** [compat.o] Error 1
make[3]: *** [all-recursive] Error 1

from https://buildd.debian.org/status/fetch.php?pkg=tor&arch=hurd-i386&ver=0.2.3.12-alpha-1&stamp=1329410988

Earlier builds that made it past this are for instance https://buildd.debian.org/status/fetch.php?pkg=tor&arch=hurd-i386&ver=0.2.3.10-alpha-1&stamp=1324069107