Fix compiler warnings about redefinition of GL_GLEXT_LEGACY

cMake/FindOpenCasCade.cmake

@@ -37,6 +37,10 @@ else(OCE_FOUND) #look for OpenCASCADE
   # we first try to find opencascade directly:
   if(NOT OCCT_CMAKE_FALLBACK)
     find_package(OpenCASCADE CONFIG QUIET)
+    get_property(flags DIRECTORY PROPERTY COMPILE_DEFINITIONS)
+    # OCCT 7.5 adds this define that causes hundreds of compiler warnings with Qt5.x, so remove it again
+    list(FILTER flags EXCLUDE REGEX [[GL_GLEXT_LEGACY]])
+    set_property(DIRECTORY PROPERTY COMPILE_DEFINITIONS ${flags})
   endif(NOT OCCT_CMAKE_FALLBACK)
   if(OpenCASCADE_FOUND)
     set(OCC_FOUND ${OpenCASCADE_FOUND})