Clang on WIndows finds VC headers instead of GCC

When I had Clang 3.7 installed it would find the STL headers from my GCC installation as long as only both those two directories in the path.

Now that I have installed Clang 3.8 the compiler keeps finding the Visual Studio headers despite the fact that it isn't even in the path

My path is as follows:

PATH=whatever;G:\Compilers\LLVM\bin;g:\compilers\Mingw64-64bit\bin