The issue is that that the Anaconda gcc on Windows is a bat file, so it can't find it. Another fix would be to use find_executable. This is because Anaconda has patched find_executalbe (which it also would be good to get backported)

diff --git Lib/distutils/spawn.py Lib/distutils/spawn.py
index b1c5a44..4703f00 100644
--- Lib/distutils/spawn.py
+++ Lib/distutils/spawn.py
@@ -156,17 +156,16 @@ def find_executable(executable, path=None):
         path = os.environ['PATH']

     paths = path.split(os.pathsep)
-    base, ext = os.path.splitext(executable)
-
-    if (sys.platform == 'win32') and (ext != '.exe'):
-        executable = executable + '.exe'
-
-    if not os.path.isfile(executable):
-        for p in paths:
-            f = os.path.join(p, executable)
-            if os.path.isfile(f):
-                # the file exists, we have a shot at spawn working
-                return f
-        return None
-    else:
-        return executable
+
+    for ext in '.exe', '.bat', '':
+        newexe = executable + ext
+
+        if os.path.isfile(newexe):
+            return newexe
+        else:
+            for p in paths:
+                f = os.path.join(p, newexe)
+                if os.path.isfile(f):
+                    # the file exists, we have a shot at spawn working
+                    return f
+    return None