fix(build-std): always link to std when testing/running proc-macros

src/cargo/core/compiler/compilation.rs

@@ -315,7 +315,10 @@ impl<'gctx> Compilation<'gctx> {
             // libs from the sysroot that ships with rustc. This may not be
             // required (at least I cannot craft a situation where it
             // matters), but is here to be safe.
-            if self.gctx.cli_unstable().build_std.is_none() {
+            if self.gctx.cli_unstable().build_std.is_none() ||
+                // Proc macros dynamically link to std, so set it anyway.
+                pkg.proc_macro()
+            {
                 search_path.push(self.sysroot_target_libdir[&kind].clone());
             }
         }

tests/build-std/main.rs

@@ -386,15 +386,7 @@ fn test_proc_macro() {
 [COMPILING] foo v0.0.0 ([ROOT]/foo)
 [FINISHED] `test` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s
 [RUNNING] unittests src/lib.rs (target/debug/deps/foo-[HASH])
-dyld[[..]]: Library not loaded: @rpath/libstd-[HASH].dylib
-  Referenced from: <[..]> [ROOT]/foo/target/debug/deps/foo-[HASH]
-  Reason: tried: '[ROOT]/foo/target/debug/deps/libstd-[HASH].dylib' (no such file), '[ROOT]/foo/target/debug/libstd-[HASH].dylib' (no such file), '/usr/local/lib/libstd-[HASH].dylib' (no such file), '/usr/lib/libstd-[HASH].dylib' (no such file, not in dyld cache)
-[ERROR] test failed, to rerun pass `--lib`
-
-Caused by:
-  process didn't exit successfully: `[ROOT]/foo/target/debug/deps/foo-[HASH]` ([..])
 
 "#]])
-        .with_status(101)
         .run();
 }