UPSTREAM: kbuild: add clang-version.sh

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

Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

Change-Id: I71ccd673392841ea99fbb76a0b41040625ebd307
(cherry picked from commit ae0c553c24c009596c3a3e903433824fe050c547)
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>