Remove DirectX SDK 10 dependency from '-opengl dynamic' builds using MinGW-W64

Hi, Everyone,

Since Qt-5.7 dropped support of MSVC versions < 2013 (see Qt Documentation) and thus Windows SDK versions < 8, same could be done for MinGW-W64. Mean no need in DirectX SDK 10 dependency for -opengl dynamic builds using MinGW-W64, when DirectX 11 toolchain added to MinGW-W64 distributions starting from version 4.9.2.
The only missing tool is Direct3D Shader Compiler 10 (fxc.exe), which could be taken from Windows SDK 8.1 or 10.

Build steps:

• in file qtbase\src\angle\src\common\common.pri change string:

  winrt|if(msvc:!win32-msvc2005:!win32-msvc2008:!win32-msvc2010){
  

  to

  winrt|msvc|if(gcc:win32) {
  

• add to %PATH% environment variable one of strings:

  %ProgramFiles(x86)%\Windows Kits\10\bin\x86
  %ProgramFiles(x86)%\Windows Kits\10\bin\x64
  %ProgramFiles(x86)%\Windows Kits\8.1\bin\x86
  %ProgramFiles(x86)%\Windows Kits\8.1\bin\x64
  

  depending of target platform and used system,

• configure and build Qt with -opengl dynamic key,

Tested for Qt-5.7 with shared+<debug,release> configurations using MinGW-W64, and all builds finished successfully. Also checked, that patch doesn't break builds using MSVC and ICC.

Still required detailed testing on real OpenGL ES applications. AFAIK, MinGW-W64 use Wine implementation of DirectX, thus could be regressions during runtime.

If proposed patch would be applied, additional changes could be made to:

• file:

  qtbase\src\angle\src\common\common.pri
  

  in order to remove became obsolete code:

  } else {
      DX_DIR = $$(DXSDK_DIR)
      isEmpty(DX_DIR) {
  	
  [snip]
  
          LIBS_PRIVATE += -L$$DXLIB_DIR
      }
  }
  

• files:

  qtbase\tools\configure\configureapp.cpp
  qtbase\tools\configure\environment.cpp
  

  in order to remove references to DXSDK_DIR variable,

• Qt Documentation in order to update requirements and build steps for -opengl dynamic builds using MinGW-W64.

Regards,
Alexander