Added ARCH_INDEPENDENT parameter to write_basic_package_version_file()

[xvitaly]

Added ARCH_INDEPENDENT parameter to write_basic_package_version_file(), because this is a architecture agnostic header-only library.

Regression caused by #879.

This PR fixes the following issue:

find_package(Microsoft.GSL CONFIG REQUIRED)

Result:

CMake Error at cmake/external/gsl/CMakeLists.txt:11 (find_package):
  Could not find a configuration file for package "Microsoft.GSL" that is
  compatible with requested version "".
  The following configuration files were considered but not accepted:
    /usr/share/cmake/Microsoft.GSL/Microsoft.GSLConfig.cmake, version: 3.1.0 (32bit)
-- Configuring incomplete, errors occurred!

If the library was built on a 32-bit host and then used on 64-bit machines (which is absolutely fine for the architecture independent libraries), it cannot be found by Cmake.

N.B. ARCH_INDEPENDENT parameter requires Cmake 3.14+.

[leha-bot]

Sorry about breakage of arch_independent.
Seems that the CMake built-in cmake_parse_arguments doesn't support generator expressions. We could try to make a LIST of arguments and conditionally append the ARCH_INDEPENDENT flag and call write_basic_package_version_file() with LIST of args.

[ghost]

All CLA requirements met.

[xvitaly]

Fixed compatibility with the ancient Cmake versions. Now it should work fine.

[JordanMaples]

Thanks for the fix.