Support multiarch in webview bootstrap

[dbnicholson]

This is essentially exactly the same as the sdl2 bootstrap.

It looks like this is all that's needed. Why it wasn't in 41c6cc0, I don't know.

[coveralls]

Pull Request Test Coverage Report for Build 2210171407

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 9 of 9 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.01%) to 61.206%

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Totals
Change from base Build 2197297205:	0.01%
Covered Lines:	4389
Relevant Lines:	6651

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💛 - Coveralls

[rtibbles]

Looks the same to me!