Rollup merge of rust-lang#149148 - davidtwco:v0-mangling-on-nightly-std, r=Kobzol

v0 mangling for std on nightly

Following rust-lang#89917 and rust-lang/compiler-team#938, it doesn't make sense that `std` for these channels would have legacy mangling while the user's code would use `v0`.

r? `@Kobzol`

Author: bend-n

src/bootstrap/src/core/builder/cargo.rs

@@ -653,6 +653,8 @@ impl Builder<'_> {
                 // If an explicit setting is given, use that
                 setting
             }
+            // Per compiler-team#938, v0 mangling is used on nightly
+            None if self.config.channel == "dev" || self.config.channel == "nightly" => true,
             None => {
                 if mode == Mode::Std {
                     // The standard library defaults to the legacy scheme