Add function to determine Linux kernel version (#27855)

This reports the kernel version (vs. the distro version) on Linux and
returns a valid Version (stripping characters like '+' which may be
present for custom-built kernels).

var/spack/repos/builtin/packages/qt/package.py

@@ -10,10 +10,11 @@
 import llnl.util.tty as tty
 
 from spack import *
+from spack.operating_systems.linux_distro import kernel_version
 from spack.operating_systems.mac_os import macos_version
 
 MACOS_VERSION = macos_version() if sys.platform == 'darwin' else None
-LINUX_VERSION = Version(platform.release()) if platform.system() == 'Linux' else None
+LINUX_VERSION = kernel_version() if platform.system() == 'Linux' else None
 
 
 class Qt(Package):