set OPENBLAS_DIR in openblas.yaml when build dependencies

I found that the numpy package is not able to find openblas at compile time, because it is looking in `$OPENBLAS_DIR/lib` and `OPENBLAS_DIR` is not set in `openblas.yaml `. I think that this setting should be unable. At least with this change numpy finds openblas for me.

Author: cmaurini

pkgs/openblas.yaml

@@ -19,3 +19,4 @@ build_stages:
 when_build_dependency:
 - {set: 'BLAS_LDFLAGS', value: '-Wl,-rpath,${ARTIFACT}/lib -L${ARTIFACT}/lib -lopenblas'}
 - {set: 'LAPACK_LDFLAGS', value: '-Wl,-rpath,${ARTIFACT}/lib -L${ARTIFACT}/lib -lopenblas'}
+- {set: 'OPENBLAS_DIR', value: '${ARTIFACT}'}