Fix C++11 narrowing error on Mac OS

Resolves #127

aesara/configdefaults.py

@@ -548,6 +548,16 @@ def add_compile_configvars():
         in_c_key=False,
     )
 
+    # Resolves C++11 narrowing error on Mac OS
+    # https://github.com/aesara-devs/aesara/issues/127
+    no_cpp_narrowing_flag = "-Wno-c++11-narrowing"
+    cxx_flags = config.gcc__cxxflags.split()
+    if sys.platform == "darwin":
+        if no_cpp_narrowing_flag not in cxx_flags:
+            cxx_flags.append(no_cpp_narrowing_flag)
+
+    config.gcc__cxxflags = " ".join(cxx_flags)
+
     config.add(
         "cmodule__warn_no_version",
         "If True, will print a warning when compiling one or more Op "