clang++: Default to c++14 std
clang++: Default to c++14 std

latest gcc7 also defaults to c++14, some packages
have started to use c++11 and newer features without
specifying -std option and rightly so now that gcc
defaults are c++14, applications can safely assume
c++14 as default

Signed-off-by: Khem Raj <729d64b6f67515e258459a5f6d20ec88b2caf8df@gmail.com>

kraj/meta-clang,kraj/meta-clang,kraj/meta-clang