changed regression test configs to --append-run-prefix for clang with libc++ (so tests run without installing clang ABI separately)
changed regression test configs to --append-run-prefix for clang with libc++ (so tests run without installing clang ABI separately)

SophistSolutions/Stroika,SophistSolutions/Stroika,SophistSolutions/Stroika,SophistSolutions/Stroika,SophistSolutions/Stroika