Add LD_PRELOAD for libsigchain.so to the environment

To remove the need to modify the bionic dynamic linker, add the
signal chaining library as a preload in the environment.  This
will be picked up by the dynamic linker and will override
sigaction and sigprocmask to allow for signal chaining.

Change-Id: I6e2d0628b009bd01e0ed9aed0b311871b9c8363a
diff --git a/rootdir/init.environ.rc.in b/rootdir/init.environ.rc.in
index 927c33d..1f964e3 100644
--- a/rootdir/init.environ.rc.in
+++ b/rootdir/init.environ.rc.in
@@ -9,3 +9,4 @@
     export ASEC_MOUNTPOINT /mnt/asec
     export LOOP_MOUNTPOINT /mnt/obb
     export BOOTCLASSPATH %BOOTCLASSPATH%
+    export LD_PRELOAD libsigchain.so