Fix cross compilation, based on OpenWRT patch.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>

diff -Nura rtorrent-0.9.2/configure.ac rtorrent-0.9.2-cross/configure.ac
--- rtorrent-0.9.2/configure.ac	2012-04-20 03:55:30.000000000 -0300
+++ rtorrent-0.9.2-cross/configure.ac	2012-05-09 11:06:49.436474039 -0300
@@ -4,7 +4,6 @@
 
 AM_INIT_AUTOMAKE
 AM_CONFIG_HEADER(config.h)
-AM_PATH_CPPUNIT(1.9.6)
 
 AC_PROG_CXX
 AC_PROG_LIBTOOL
diff -Nura rtorrent-0.9.2/scripts/common.m4 rtorrent-0.9.2-cross/scripts/common.m4
--- rtorrent-0.9.2/scripts/common.m4	2012-03-13 09:10:49.000000000 -0300
+++ rtorrent-0.9.2-cross/scripts/common.m4	2012-05-09 11:05:56.620102678 -0300
@@ -223,7 +223,7 @@
 AC_DEFUN([TORRENT_CHECK_EXECINFO], [
   AC_MSG_CHECKING(for execinfo.h)
 
-  AC_RUN_IFELSE([AC_LANG_SOURCE([
+  AC_LINK_IFELSE([AC_LANG_SOURCE([
       #include <execinfo.h>
       int main() { backtrace((void**)0, 0); backtrace_symbols((char**)0, 0); return 0;}
       ])],