Consider using -dumpversion instead of --version for detecting compiler version

The compiler being used by me on --version, throws the following output:

x86_64-conda_cos6-linux-gnu-cc (crosstool-NG 1.23.0.449-a04d0) 7.3.0                                                                                                                        
Copyright (C) 2017 Free Software Foundation, Inc.                                                                                                                                                                  
This is free software; see the source for copying conditions.  There is NO                                                                                                                                         
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

The regex parsing in the macro _vtk_test_compiler_hidden_visibility in CMake/VTKGenerateExportHeader.cmake fails, because then it sets gcc_version to 3.0.449 instead of 7.3.0 and makes the assumption that the compiler is too old and ends up generating header files with no (blank) values for DEFINE_EXPORT, DEFINE_IMPORT and DEFINE_NO_EXPORT

Why use --version, instead of just -dumpversion or CMAKE_CXX_COMPILER_VERSION ?