While Trying to install VirtualBox from AUR, and when installing the dependencies, I got this error.

==> Starting build()...
/tmp/yaourt-tmp-keripix/aur-libpng12/libpng12/./PKGBUILD: line 26: patch: command not found
==> ERROR: Build Failed.
Aborting...
Error: Makepkg was unable to build libpng12 package.

It was solved by install base-devel package

sudo pacman -Sy base-devel

So, as a note to me, keep in mind that to install “build” packages from AUR, base-devel package is needed.