Rollup merge of #155935 - paradoxicalguy:fix-out-dir-remap, r=Urgau,

remap OUT_DIR paths to fix build script path leakage in crate metadata.

### problem:
- build script outputs (`OUT_DIR`) leak absolute paths into crate metadata causing non-determinism across identical builds.
- bootstrap remaps source paths (`self.build.src`) and registry sources but doesn't not remap `self.build.out` used by `OUT_DIR`

### fix:
- adding `--remap-path-prefix` for `self.build.out` , mapping it to a stable virtual prefix, consistent with existing remappings

### result:
- removes path-based non-determinism from build script outputs
- verified via stage 2 reproducibility testing.

r? @Urgau

Author: jhpratt

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

@@ -1073,6 +1073,8 @@ impl Builder<'_> {
                         // rustc creates absolute paths (in part bc of the `rust-src` unremap
                         // and for working directory) so let's remap the build directory as well.
                         format!("{}={map_to}", self.build.src.display()),
+                        // remap OUT_DIR so they don't leak into artifacts.
+                        format!("{}={map_to}/out", self.build.out.display()),
                     ]
                     .join("\t");
                     cargo.env("RUSTC_DEBUGINFO_MAP", map);
@@ -1093,6 +1095,8 @@ impl Builder<'_> {
                         // rustc creates absolute paths (in part bc of the `rust-src` unremap
                         // and for working directory) so let's remap the build directory as well.
                         format!("{}={map_to}", self.build.src.display()),
+                        // remap OUT_DIR so they don't leak into artifacts.
+                        format!("{}={map_to}/out", self.build.out.display()),
                     ]
                     .join("\t");
                     cargo.env("RUSTC_DEBUGINFO_MAP", map);