Provide setup.py option to profile Cython code (dask#4362)

As it can be useful for development to profile the Cythonized code and
this requires an argument be provided to the extensions to enable, go
ahead and add some logic to `setup.py` to parse this option if provided.
If it is not provided, profiling is turned off, which is preferable as
this would impact the performance of the compiled code.

Author: jakirkham

setup.py

@@ -21,19 +21,27 @@
     else:
         install_requires.append(r)
 
-try:
-    sys.argv.remove("--with-cython")
-    cython = True
-except ValueError:
-    cython = False
+cython_arg = None
+for i in range(len(sys.argv)):
+    if sys.argv[i].startswith("--with-cython"):
+        cython_arg = sys.argv[i]
+        del sys.argv[i]
+        break
 
 ext_modules = []
-if cython:
+if cython_arg:
     try:
-        import cython
+        import cython  # noqa: F401
     except ImportError:
         setup_requires.append("cython")
 
+    profile = False
+    try:
+        _, param = cython_arg.split("=")
+        profile = param == "profile"
+    except ValueError:
+        pass
+
     cyext_modules = [
         Extension(
             "distributed.scheduler",
@@ -46,6 +54,7 @@
             "binding": False,
             "embedsignature": True,
             "language_level": 3,
+            "profile": profile,
         }
     ext_modules.extend(cyext_modules)