Support gcc versions up to 9.X

CMake/VTKGenerateExportHeader.cmake

@@ -174,7 +174,7 @@ macro(_vtk_test_compiler_hidden_visibility)
     execute_process(COMMAND ${CMAKE_C_COMPILER} --version
       OUTPUT_VARIABLE _gcc_version_info
       ERROR_VARIABLE _gcc_version_info)
-    string(REGEX MATCH "[3456]\\.[0-9]\\.[0-9]*"
+    string(REGEX MATCH "[3-9]\\.[0-9]\\.[0-9]*"
       _gcc_version "${_gcc_version_info}")
     # gcc on mac just reports: "gcc (GCC) 3.3 20030304 ..." without the
     # patch level, handle this here:

CMake/vtkCompilerExtras.cmake

@@ -32,7 +32,7 @@ if(CMAKE_COMPILER_IS_GNUCXX)
     OUTPUT_VARIABLE _gcc_version_info
     ERROR_VARIABLE _gcc_version_info)
 
-  string (REGEX MATCH "[3456]\\.[0-9]\\.[0-9]*"
+  string (REGEX MATCH "[3-9]\\.[0-9]\\.[0-9]*"
     _gcc_version "${_gcc_version_info}")
   if(NOT _gcc_version)
     string (REGEX REPLACE ".*\\(GCC\\).*([34]\\.[0-9]).*" "\\1.0"