Add explicit build-time dependencies on some tools so that superenv puts them in the path. (And also so they'll be installed because they are needed!) Fixes Homebrew/homebrew#15145.
Fixes Homebrew/homebrew#15145.
Intended to be used by glib-networking, coming in a later commit. Closes Homebrew/homebrew#14240. Signed-off-by: Jack Nagel <jacknagel@gmail.com>