Append to ARCHFLAGS instead of overwriting it (#169)

Append to `ARCHFLAGS` instead of overwriting it

Author: pierreluctg

setup.py

@@ -102,7 +102,7 @@ def run(self):
     compile_args = GCC_COMPILE_ARGS
 elif "DARWIN" in platform.system().upper():
     # Mac doesn't respect the compiler args, but will append with ARCHFLAGS environment variable
-    os.environ["ARCHFLAGS"] = "-std=c++17"
+    os.environ["ARCHFLAGS"] += " -std=c++17"
     compile_args = []
 else:
     compile_args = []