( @Akien : this PR is for current HEAD only, not to be cherry-picked for 2.1.1 )
this is manual revertion of #6501 which introduced a bug that prevented
scons from detecting Mingw under Windows when MSVC was installed.
(thanks to @vnen for finding this)
AND
it fixes the actual bug that prevented scons from detecting MSVC standalone
compiler ( a confusions between ``VSINSTALLDIR`` and ``VCINSTALLDIR`` )
The freeware Standalone MSVC C++ Build Tools are available here :
http://landinghub.visualstudio.com/visual-cpp-build-tools