cmake: Make enable_language() clear about what it is actually doing

That call to enable_languages() is passed C CXX ASM which misleads the
reader into thinking that the three languages are enabled in that call but
at that point only ASM is actually because C and CXX were already
implicitly enabled by the call to project() above. The suggested change
removes the misleading C CXX arguments but we could as well make it clear
in the project() call by passing LANGUAGES C CXX.

Signed-off-by: Nicolas Lebedenco <nicolas@lebedenco.net>