Add support for Linux ARM64

[dlon]

This makes it possible to build the app for Linux ARM. It can be done either via cross-compilation or by building it on an ARM host (with the caveat that grpc-tools will refuse to generate code for the management interface .proto (#2500) in the latter case).

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This change is 

[pinkisemils]

Reviewed 1 of 1 files at r1, 1 of 1 files at r2, 1 of 1 files at r3, 1 of 1 files at r4, 1 of 1 files at r5, 2 of 2 files at r6.
Reviewable status: 4 of 8 files reviewed, 1 unresolved discussion (waiting on @dlon and @pinkisemils)

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build.sh line 209 at r7 (raw file):

    local current_target=${1:-""}
    local for_target_string=""
    local stripbin="strip"

I presume this script wouldn't be supposed to be ran on anything but our own build machines? Because if it was running on an ARM host, then it would be nice if the strip binary could be specified via an environment variable or via some other way. Or the script could just detect that and use regular strip instead of the cross-compiled one. Or am I horribly misinterpreting what's going on here? 😅

[pinkisemils]

Aside from the strip path, this !

Reviewed 1 of 1 files at r7, 1 of 1 files at r8, 1 of 1 files at r9, 1 of 1 files at r10, all commit messages.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @dlon)

[dlon]

Reviewable status: 7 of 8 files reviewed, 1 unresolved discussion (waiting on @pinkisemils)

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build.sh line 209 at r7 (raw file):

Previously, pinkisemils (Emīls Piņķis) wrote…

I presume this script wouldn't be supposed to be ran on anything but our own build machines? Because if it was running on an ARM host, then it would be nice if the strip binary could be specified via an environment variable or via some other way. Or the script could just detect that and use regular strip instead of the cross-compiled one. Or am I horribly misinterpreting what's going on here? 😅

Done. You don't have to specify TARGETS if host equals the target, but it should work regardless.

[pinkisemils]

Reviewed 3 of 3 files at r11, all commit messages.
Reviewable status: all files reviewed, 2 unresolved discussions (waiting on @dlon)

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build.sh line 214 at r11 (raw file):

        local arch="$(uname -m)"
        if [[ "$current_target" == "aarch64-unknown-linux-gnu" && "${arch,,}" != "aarch64" ]]; then

I think in this case the arch variable might well be inlined like "$(uname -m)" != "aarch64".

[pinkisemils]

Reviewed 1 of 1 files at r12, all commit messages.
Reviewable status: all files reviewed, 2 unresolved discussions (waiting on @dlon)