Arch Linux

I've got to ask, why? Would would be the point?

There are a LOT of build options hard-wired into the binary, and no way (AFAIK) to list them from the command line.

If curious, see http://hostap.epitest.fi/cgit/hostap/tree/wpa_supplicant/defconfig

Some you might want to know:
CONFIG_IEEE80211W
CONFIG_IEEE80211R
CONFIG_IEEE80211N
CONFIG_IEEE80211AC
CONFIG_AP
CONFIG_P2P
CONFIG_TDLS

OK, but the config file is easily accessible via the website, Git, SVN, or the ABS. What would installing it to the filesystem accomplish?

Arch uses a modified build config, which I looked for but couldn't find.

And looking online would give you the most current file, but not necessarily what you've got installed.

As I said, it's available from the website: https://www.archlinux.org/packages/core/x86_64/wpa_supplicant/ (Source Files link on the right)
From Git: git://projects.archlinux.org/svntogit/packages.git
From SVN: https://www.archlinux.org/svn/ (this link is on the front page)
And from the ABS: https://wiki.archlinux.org/index.php/Arch_Build_System

Most of the package in the repos have some kind of build time configuration, do you expect them all to install their build script?

As for it being the latest and not what is installed, every one of these gives you access to testing and core files separately, and Git and SVN have historical data. You should have the latest installed, anyway, so the whole thing is moot.

Ah I didn't see the source files link previously.

If you can't find out what's hard-wired via the command line, documenting the compile-time features is really helpful.