cmake: fix for GCC 6.x

cmake/OpenCVPCHSupport.cmake

@@ -14,12 +14,7 @@
 
 IF(CMAKE_COMPILER_IS_GNUCXX)
 
-    EXEC_PROGRAM(
-        ${CMAKE_CXX_COMPILER}
-        ARGS ${CMAKE_CXX_COMPILER_ARG1} -dumpversion
-        OUTPUT_VARIABLE gcc_compiler_version)
-    #MESSAGE("GCC Version: ${gcc_compiler_version}")
-    IF(gcc_compiler_version VERSION_GREATER "4.2.-1" AND gcc_compiler_version VERSION_LESS "6.0.0")
+    IF(NOT CMAKE_CXX_COMPILER_VERSION VERSION_LESS "4.2.0")
         SET(PCHSupport_FOUND TRUE)
     ENDIF()
 

cmake/OpenCVUtils.cmake

@@ -41,6 +41,9 @@ function(ocv_include_directories)
     get_filename_component(__abs_dir "${dir}" ABSOLUTE)
     if("${__abs_dir}" MATCHES "^${OpenCV_SOURCE_DIR}" OR "${__abs_dir}" MATCHES "^${OpenCV_BINARY_DIR}")
       list(APPEND __add_before "${dir}")
+    elseif(CMAKE_COMPILER_IS_GNUCXX AND NOT CMAKE_CXX_COMPILER_VERSION VERSION_LESS "6.0" AND
+           dir MATCHES "/usr/include$")
+      # workaround for GCC 6.x bug
     else()
       include_directories(AFTER SYSTEM "${dir}")
     endif()