Pass "-m opt" on Linux/Mac in buck2.py

Summary: Testing if this helps with perf, as recently I moved usage from `buck2.sh` to `buck2.py` and the buck2 CI perf got affected.

Reviewed By: JakobDegen

Differential Revision: D67291815

fbshipit-source-id: 06a04cb264fd65d494e8abc10e77dd240ca71a20

buck2.py

@@ -36,7 +36,7 @@ def get_extra_build_params(args: argparse.Namespace) -> List[str]:
     if system_platform == "Windows":
         return ["@fbcode//mode/opt-win"]
 
-    params = []
+    params = ["-m", "opt"]
 
     arch_platform = platform.machine()
     if arch_platform == "x86_64":