On 64-bit windows-msvc, can't specify SysV calling convention

[jethrogb]

On most 64-bit platforms you can use extern "C" to select the SysV calling convention or extern "win64" to select the Microsoft calling convention. On windows-msvc, extern "C" is the same as extern "win64" and there's no way to select SysV.

[retep998]

Are there any situations where you'd want the SysV calling convention on Windows?

[Aatch]

@retep998 interfacing with assembly seems like a reasonable use-case.

[CensoredUsername]

@retep998 It's an annoyance/restriction when writing anything that deals with run-time assembling (JIT compilers for instance). It necessitates using of the asm feature to call into it or sticking to win64 as calling convention on all platforms.

Alternatively large parts of such code must be duplicated in order to deal with the different register allocations

[CensoredUsername]

This is available now since the merge of #34494, this issue can be closed in favor of the tracking issue.