Mingw builds fail about copper

[atollk]

Running the Mingw tests on a commit on which they passed three weeks ago now causes a segfault for unknown reasons:

Run ctest -C Release --output-on-failure --timeout 240
  ctest -C Release --output-on-failure --timeout 240
  shell: D:\a\_temp\msys\msys2.CMD {0}
  env:
    MSYSTEM: MINGW64
Test project /d/a/copper/copper/build
    Start 1: copper_tests
1/1 Test #1: copper_tests .....................***Exception: SegFault  0.04 sec
Errors while running CTest


0% tests passed, 1 tests failed out of 1

Total Test time (real) =   0.05 sec

The following tests FAILED:
	  1 - copper_tests (SEGFAULT)

Therefore, clang Mingw was disabled for the time being.