Fixes VTK 7.0.0 compilation with GCC 6.1.1

fix_gcc_visibility_check.patch

Index: CMake/GenerateExportHeader.cmake
===================================================================
--- a/CMake/GenerateExportHeader.cmake
+++ b/CMake/GenerateExportHeader.cmake
@@ -163,19 +163,7 @@ endmacro()
 macro(_test_compiler_hidden_visibility)
 
   if(CMAKE_COMPILER_IS_GNUCXX)
-    execute_process(COMMAND ${CMAKE_C_COMPILER} ARGS --version
-      OUTPUT_VARIABLE _gcc_version_info
-      ERROR_VARIABLE _gcc_version_info)
-    string(REGEX MATCH "[345]\\.[0-9]\\.[0-9]*"
-      _gcc_version "${_gcc_version_info}")
-    # gcc on mac just reports: "gcc (GCC) 3.3 20030304 ..." without the
-    # patch level, handle this here:
-    if(NOT _gcc_version)
-      string(REGEX REPLACE ".*\\(GCC\\).*([34]\\.[0-9]).*" "\\1.0"
-        _gcc_version "${_gcc_version_info}")
-    endif()
-
-    if(${_gcc_version} VERSION_LESS "4.2")
+    if(CMAKE_CXX_COMPILER_VERSION VERSION_LESS "4.2")
       set(GCC_TOO_OLD TRUE)
     endif()
   endif()
Index: CMake/vtkCompilerExtras.cmake
===================================================================
--- a/CMake/vtkCompilerExtras.cmake
+++ b/CMake/vtkCompilerExtras.cmake
@@ -27,24 +27,12 @@ if(CMAKE_COMPILER_IS_GNUCXX)
       "${VTK_EXTRA_SHARED_LINKER_FLAGS} -Wl,--no-undefined -lc ${CMAKE_SHARED_LINKER_FLAGS}")
   endif()
 
-  # Now check if we can use visibility to selectively export symbols
-  execute_process(COMMAND ${CMAKE_C_COMPILER} ARGS --version
-    OUTPUT_VARIABLE _gcc_version_info
-    ERROR_VARIABLE _gcc_version_info)
-
-  string (REGEX MATCH "[345]\\.[0-9]\\.[0-9]*"
-    _gcc_version "${_gcc_version_info}")
-  if(NOT _gcc_version)
-    string (REGEX REPLACE ".*\\(GCC\\).*([34]\\.[0-9]).*" "\\1.0"
-      _gcc_version "${_gcc_version_info}")
-  endif()
-
   # GCC visibility support, on by default and in testing.
   check_cxx_compiler_flag(-fvisibility=hidden HAVE_GCC_VISIBILITY)
   option(VTK_USE_GCC_VISIBILITY "Use GCC visibility support if available." OFF)
   mark_as_advanced(VTK_USE_GCC_VISIBILITY)
 
-  if(${_gcc_version} VERSION_GREATER 4.2.0 AND BUILD_SHARED_LIBS
+  if(CMAKE_CXX_COMPILER_VERSION VERSION_GREATER 4.2.0 AND BUILD_SHARED_LIBS
     AND HAVE_GCC_VISIBILITY AND VTK_USE_GCC_VISIBILITY
     AND NOT MINGW AND NOT CYGWIN)
     # Should only be set if GCC is newer than 4.2.0

Successfully compiled vtk6 on CentOS 8 (GCC 8) ,good job !@rafamanzo