Difficulty building OpenCV with MinGW

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I'm trying to build OpenCV 4.1.1 with MinGW32 from the source (in Windows 10 and for C++). I've been following the instructions at the bottom of this page: https://docs.opencv.org/master/d3/d52... and at the top of this page: http://eyalarubas.com/opencv-installa.... So far I've successfully cloned the source, but when I press "configure" in CMake I get several errors: "Could not find openBLAS include","A library with LAPACK API not found"

The only option I had changed was to enable "ENABLE_SOLUTION_FOLDERS" as instructed in the first link. CMake still allowed me to continue and "generate", however then when I typed "mingw32-make" into the command prompt it gave me more significant errors at about 20%: "Error: 'mutex' in namespace 'std' does not have a type"

I then disabled openexr as this seemed to be the source of the error and tried again, but it didn't get much further: "Error: '::_wfopen' has not been declared"

I don't know whether they are to do with the warnings I was getting in CMake, or whether it's something else. What should I do now?