cmake should link openblas with -lopenblas

[ghost]

Currently if you build with cmake and LLAMA_OPENBLAS=ON it does not link the OpenBlas library properly and the build fails. This add OpenBlas linking to cmake like how it's done in the Makefile LDFLAGS (below).

ifdef LLAMA_OPENBLAS
    CFLAGS  += -DGGML_USE_OPENBLAS -I/usr/local/include/openblas
    LDFLAGS += -lopenblas

[sw]

Thanks. I can confirm the link failure and that this fixes it.