[mpact][compiler] enable clients to set opt level and support library

Done through the enviroment. For example

export OPT_LEVEL=3
epport SUPPORT_LIB=<path to lib.so>

python/mpact/mpactbackend.py

diff --git a/python/mpact/mpactbackend.py b/python/mpact/mpactbackend.py
index 80b58df..2a01af2 100644
--- a/python/mpact/mpactbackend.py
+++ b/python/mpact/mpactbackend.py
@@ -1,5 +1,6 @@
 import ctypes
 import numpy as np
+import os
 import torch
 
 from typing import Any, Callable, Optional, Tuple, Dict
@@ -17,6 +18,11 @@
     LinalgOnTensorsBackend,
 )
 
+# One time set up of support library and optimization level.
+SUPPORT_LIB = os.getenv("SUPPORT_LIB", default=None)
+SHARED_LIBS = [  ] if SUPPORT_LIB is None else [ SUPPORT_LIB ]
+OPT_LEVEL = int(os.getenv("OPT_LEVEL", default=2))
+
 
 def assert_arg_type_is_supported(ty):
     SUPPORTED = [
@@ -95,8 +101,10 @@
 
 
 class MpactBackendInvoker:
-    def __init__(self, module, opt_level=2, shared_libs=[]):
-        self.ee = ExecutionEngine(module, opt_level=opt_level, shared_libs=shared_libs)
+    def __init__(self, module):
+        self.ee = ExecutionEngine(
+            module, opt_level=OPT_LEVEL, shared_libs=SHARED_LIBS
+        )
         self.result = None
 
         return_funcs = get_return_funcs(module)