Suppress virtualenv warning messages on Windows

Suppress 'WARNING: Attempting to work in a virtualenv...' message
on Windows in bash and PowerShell.  Adapts
pip.locations.running_under_virtualenv for use in no sys.executable
symlinks case.

IPython/core/interactiveshell.py

@@ -732,6 +732,16 b' class InteractiveShell(SingletonConfigurable):'
             # Not in a virtualenv
             return
         
+        # Handle no symbolic link case first.
+        if not os.path.islink(sys.executable):
+            # Adapted from pip.locations.running_under_virtualenv
+            if hasattr(sys, 'real_prefix'):
+                # Running properly in a virtualenv
+                return
+            elif sys.prefix != getattr(sys, "base_prefix", sys.prefix):
+                # Running properly in a venv
+                return
+
         # venv detection:
         # stdlib venv may symlink sys.executable, so we can't use realpath.
         # but others can symlink *to* the venv Python, so we can't just use sys.executable.