make use of configure substitution and document non-warning CXX flags and Vc branch
make use of configure substitution and document non-warning CXX flags and Vc branch

chr-engwer/Vc,VcDevel/Vc,chr-engwer/Vc,VcDevel/Vc,VcDevel/Vc,VcDevel/Vc,chr-engwer/Vc