clang.bbclass: Set CCACHE_COMPILERCHECK as default value
clang.bbclass: Set CCACHE_COMPILERCHECK as default value

oe-core's ccache.bbclass contains:

 export CCACHE_COMPILERCHECK ?= "%compiler% -dumpspecs"

which sets a default value and allows others to easily override the
value of CCACHE_COMPILERCHECK if they wish to. Let's update
clang.bbclass to also set only the default value of CCACHE_COMPILERCHECK
too.

Signed-off-by: Mike Crowe <347ead6348e936507920c15d2ae8266ac6ce9b49@mcrowe.com>

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