If you compile rsyslog from git on CentOS 5 you run into the trouble that
fails, telling you that autotools 2.59 provided by CentOS is too old.
The solution to this problem is to install version 2.61 of autotools. You will probably not want to overwrite the default CentOS package, so you should install it in some alternate location (e.g. /opt) and include that location in the topmost spot of your path. all this can be done as follows:
tar xjf autoconf-2.61.tar.bz2
sudo make install
Then, you need to change your path, for example as follows (this is obviously a temporary alteration!):
After these changes, you should be able to run autoreconf for rsyslog.