Autotools: Use built-in shell tests and exec autoreconf

Signed-off-by: Chris Dickens <christopher.a.dickens@gmail.com>
diff --git a/bootstrap.sh b/bootstrap.sh
index dc56539..cfd2b45 100755
--- a/bootstrap.sh
+++ b/bootstrap.sh
@@ -1,6 +1,8 @@
 #!/bin/sh
 
-if ! test -d m4 ; then
+set -e
+
+if [ ! -d m4 ]; then
     mkdir m4
 fi
-autoreconf -ivf || exit 1
+exec autoreconf -ivf