[Executorch][Kernels] Build optimized lib with -O2

Dont rely on top level config for optimization and rather set our own for optimized kernels

Differential Revision: [D64910575](https://our.internmc.facebook.com/intern/diff/D64910575/)

[ghstack-poisoned]

Author: kimishpatel

kernels/optimized/lib_defs.bzl

@@ -121,6 +121,7 @@ def define_libs():
             exported_headers = native.glob([
                 "blas/**/*.h",
             ]),
+            compiler_flags = ["-O2"],
             header_namespace = "executorch/kernels/optimized",
             visibility = [
                 "//executorch/...",

kernels/optimized/op_registration_util.bzl

@@ -87,7 +87,7 @@ def define_op_library(name, deps):
         ],
         # kernels often have helpers with no prototypes just disabling the warning here as the headers
         # are codegend and linked in later
-        compiler_flags = ["-Wno-missing-prototypes"],
+        compiler_flags = ["-Wno-missing-prototypes", "-O2"],
         deps = [
             "//executorch/runtime/kernel:kernel_includes",
         ] + augmented_deps,