Merge pull request #5462 from alalek:fix_x86_detection

cmake/OpenCVDetectCXXCompiler.cmake

@@ -116,6 +116,12 @@ elseif(CMAKE_SYSTEM_PROCESSOR MATCHES "^(aarch64.*|AARCH64.*)")
   set(AARCH64 1)
 endif()
 
+# Workaround for 32-bit operating systems on 64-bit x86_64 processor
+if(X86_64 AND CMAKE_SIZEOF_VOID_P EQUAL 4 AND NOT FORCE_X86_64)
+  message(STATUS "sizeof(void) = 4 on x86 / x86_64 processor. Assume 32-bit compilation mode (X86=1)")
+  unset(X86_64)
+  set(X86 1)
+endif()
 
 # Similar code exists in OpenCVConfig.cmake
 if(NOT DEFINED OpenCV_STATIC)