[PATCH 1/3] build: Check for -Wimplicit-fallthrough=5 separately

[Mark Wielaard]

Hi Timm,

On Wed, 2021-02-17 at 10:27 +0100, Timm Bäder via Elfutils-devel wrote:
> GCC accepts the =5, which means it doesn't try to parse any comments
> and only accepts the fallthrough attribute in code. Clang does not ever
> parse any comments and always wants the fallthrough attribute anyway.
> Clang also doesn't accept the =n parameter for -Wimplicit-fallthrough.
> 
> Test for =5 separately and use it if supported and fall back to just
> -Wimplicit-fallthrough otherwise.

Looks good, pushed.

Thanks,

Mark