How to overcome "'aclocal-1.15' is missing on your system" warning?
Before running ./configure try running autoreconf -f -i. The autoreconf program automatically runs autoheader, aclocal, automake, autopoint and libtoolize as required.
Edit to add: This is usually caused by checking out code from Git instead of extracting it from a .zip or .tar.gz archive. In order to trigger rebuilds when files change, Git does not preserve files' timestamps, so the configure script might appear to be out of date. As others have mentioned, there are ways to get around this if you don't have a sufficiently recent version of autoreconf.
Another edit: This error can also be caused by copying the source folder extracted from an archive with scp to another machine. The timestamps can be updated, suggesting that a rebuild is necessary. To avoid this, copy the archive and extract it in place.
Often, you don't need any auto* tools and the simplest solution is to simply run touch aclocal.m4 configure in the relevant folder (and also run touch on Makefile.am and Makefile.in if they exist). This will update the timestamp of aclocal.m4 and remind the system that aclocal.m4 is up-to-date and doesn't need to be rebuilt. After this, it's probably best to empty your build directory and rerun configure from scratch after doing this. I run into this problem regularly. For me, the root cause is that I copy a library (e.g. mpfr code for gcc) from another folder and the timestamps change.
Of course, this trick isn't valid if you really do need to regenerate those files, perhaps because you have manually changed them. But hopefully the developers of the package distribute up-to-date files.
And of course, if you do want to install automake and friends, then use the appropriate package-manager for your distribution.
Install aclocal which comes with automake:
brew install automake # for Mac
apt-get install automake # for Ubuntu
Try again:
./configure && make