toolchain: Unbuffer build tool messages

Author: hbirchtree

toolchain/building.py

@@ -267,7 +267,7 @@ def _absorb_shell_env(self, script: Path) -> None:
 
 
 def _banner(msg: str) -> None:
-    print(f"\n:: {msg}")
+    print(f"\n:: {msg}", flush=True)
 
 
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