Use -O2 compilation for Autocorrect only (#15583)

Summary:
Pull Request resolved: #15583

Apply -02 compiler flag to make FLLM autocorrect faster

Sheet measuring different scopes of applying -02 and the resulting latency
https://docs.google.com/spreadsheets/d/1ZnxoRwCIiMz3hXyhgb6sm_2UThBUyq-mpp8RzksfJMQ/edit?usp=sharing

****Latency****

Reviewed By: BlakeLucchesi, lucylq

Differential Revision: D85152814

Author: chandanjain999

shim_et/xplat/executorch/build/runtime_wrapper.bzl

@@ -117,6 +117,12 @@ def _patch_build_mode_flags(kwargs):
             "ovr_config//os:macos": ["-fvisibility=default"],
     })
 
+    # Add -O2 compiler flag when the compiler_flag_O2 config is set
+    kwargs["compiler_flags"] = kwargs["compiler_flags"] + select({
+        "DEFAULT": [],
+        # @oss-disable: "fbsource//xplat/assistant/oacr/native/scripts:compiler_flag_O2": ["-O2"],
+    })
+
     return kwargs
 
 def _patch_test_compiler_flags(kwargs):