scons/MSYS2-MinGW-W64: Fix build options defaults
When building in a MSYS2 Mingw-w64 environment Mesa3D sets wrong default build options which inevitably lead to build failure.
Edited by Prodea Alexandru-Liviu
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When building in a MSYS2 Mingw-w64 environment Mesa3D sets wrong default build options which inevitably lead to build failure.