std.os.uefi: Fix calling convention build error

```
std/os/uefi/protocol/simple_text_input.zig:10:63: error: no field named 'Win64' in enum '@typeInfo(builtin.CallingConvention).@"union".tag_type.?'
std/builtin.zig:169:31: note: enum declared here
std/os/uefi/protocol/simple_text_output.zig:9:64: error: no field named 'Win64' in enum '@typeInfo(builtin.CallingConvention).@"union".tag_type.?'
std/builtin.zig:169:31: note: enum declared here
std/os/uefi/tables/runtime_services.zig:26:86: error: no field named 'Win64' in enum '@typeInfo(builtin.CallingConvention).@"union".tag_type.?'
std/builtin.zig:169:31: note: enum declared here
```
5769592cddLinus Groh committed on 10/25/2024, 8:45:55 AM· committed by Alex Rønne Petersenparent56996a2
1 file changedLine totals unavailable