always obey GEVENT_NO_CFFI_BUILD (gevent#979)

If libev is not embedded, we still want to set GEVENT_NO_CFFI_BUILD=1 to
prevent setup.py from trying to configure libev, regardless whether cffi
modules will actually be built or not.

setup.py

@@ -90,16 +90,17 @@
 except ImportError:
     pass
 else:
-    if IGNORE_CFFI and not PYPY:
-        # Allow distributors to turn off CFFI builds
-        # even if it's available, because CFFI always embeds
-        # our copy of libev and they may not want that.
-        del cffi_modules[:]
     # Note that we don't add cffi to install_requires, it's
     # optional. We tend to build and distribute wheels with the CFFI
     # modules built and they can be imported if CFFI is installed.
     # install_requires.append('cffi >= 1.3.0')
+    pass
 
+if IGNORE_CFFI and not PYPY:
+    # Allow distributors to turn off CFFI builds
+    # even if it's available, because CFFI always embeds
+    # our copy of libev and they may not want that.
+    del cffi_modules[:]
 
 # If we are running info / help commands, or we're being imported by
 # tools like pyroma, we don't need to build anything