Clear MSVC SCons cache

After we patch the SCons code to find our WINE
installation, clear the MSVC cache so that if SCons
already checked for MSVC, we force it to check again.

tools/__init__.py

@@ -90,6 +90,12 @@ def _wine_read_reg64(value, hkroot=None):
             SCons.Tool.MSCommon.common.read_reg = _wine_read_reg64
         else:
             SCons.Tool.MSCommon.common.read_reg = _wine_read_reg32
+        # Clear cache to force detection of MSVC again
+        try:
+            import SCons.Tool.MSCommon.vc
+        except ImportError:
+            return
+        setattr(SCons.Tool.MSCommon.vc, '__INSTALLED_VCS_RUN', None)
 
 def _get_python_include(env):
     """Get the directory containing Python.h"""