Auto-detect non-x86 Linux systems on Download page

[harding]

The big blue button on the download page uses the browser user agent string to recommend a binary for the user to download. Presently it only recommends x86 binaries for Linux users. Either it should also recommend ARM and RISCV binaries for those users or we should just get rid of the button and so encourage users to select their own platform.

List of popular browser strings to test matching against: https://www.whatismybrowser.com/detect/what-is-my-user-agent

Help needed: I don't see any browser strings on the above list for RISCV. Does X11 run on that platform? If so, anyone running a graphical browser could help by replying with their browser string (e.g. as reported here).

Previous discussion: https://github.com/bitcoin-core/bitcoincore.org/pull/695#pullrequestreview-354439276

[katesalazar]

Presently it only recommends x86 binaries for Linux users. Either it should also recommend ARM and RISCV binaries for those users or we should just get rid of the button and so encourage users to select their own platform.

I think it should recommend all of x86, ARM, RISCV, whatnot, Linux binaries (maybe ordered by "common sense", dunno), until you find the way to reliably detect the computer type/architecture. I would suggest not removing the big blue button. I think there can't be three links in the button, so the hell with it and add as many big blue buttons as architectures.

The architecture problem hitting Apple as well is imminent, I suppose.

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BTW my resolution totally wrecks the big blue button off.

Typical:

Artificially enlarged:

Will try to tweak and if get anything interesting add ticket and PR.