rt.backtrace.dwarf: Add support for DWARF v4 & 64-bit DWARF and fix non-x86 alignment issues

[kinke]

Part of LDC since v1.10 (and has been rotting here upstream as part of #2151 for almost a year now).

[dlang-bot]

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[thewilsonator]

cc @CyberShadow whats with the ae failure? Looks unrelated, please doublecheck and merge if all good. Ah, I see it fails elsewhere too.

[CyberShadow]

@thewilsonator Yes, see dlang/dmd#9618 (comment)