FROMLIST: kbuild: add clang-version.sh

Based on gcc-version.sh, clang-version.sh prints out the correct
version of clang.

Bug: 62093296
Bug: 67506682
Change-Id: I399ed4cfbe30f6ac93e519abd84dd4c7cb96e32c
(am from https://patchwork.kernel.org/patch/10085763/

)
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>