TST: fix running the test suite in builds without BLAS/LAPACK

This was broken with `undefined symbol: dlapy3_` because the test
suite imports `linalg.lapack_lite` directly. See numpygh-24200 for more
details.

numpy/linalg/tests/test_linalg.py

@@ -21,6 +21,13 @@
     assert_almost_equal, assert_allclose, suppress_warnings,
     assert_raises_regex, HAS_LAPACK64, IS_WASM
     )
+try:
+    import numpy.linalg.lapack_lite
+except ImportError:
+    # May be broken when numpy was built without BLAS/LAPACK present
+    # If so, ensure we don't break the whole test suite - the `lapack_lite`
+    # submodule should be removed, it's only used in two tests in this file.
+    pass
 
 
 def consistent_subclass(out, in_):

numpy/linalg/umath_linalg.cpp

@@ -4597,5 +4597,11 @@ PyMODINIT_FUNC PyInit__umath_linalg(void)
         return NULL;
     }
 
+#ifdef HAVE_BLAS_ILP64
+    PyDict_SetItemString(d, "_ilp64", Py_True);
+#else
+    PyDict_SetItemString(d, "_ilp64", Py_False);
+#endif
+
     return m;
 }

numpy/testing/_private/utils.py

@@ -22,7 +22,7 @@
 from numpy.core import (
      intp, float32, empty, arange, array_repr, ndarray, isnat, array)
 from numpy import isfinite, isnan, isinf
-import numpy.linalg.lapack_lite
+import numpy.linalg._umath_linalg
 
 from io import StringIO
 
@@ -54,7 +54,7 @@ class KnownFailureException(Exception):
 IS_PYPY = sys.implementation.name == 'pypy'
 IS_PYSTON = hasattr(sys, "pyston_version_info")
 HAS_REFCOUNT = getattr(sys, 'getrefcount', None) is not None and not IS_PYSTON
-HAS_LAPACK64 = numpy.linalg.lapack_lite._ilp64
+HAS_LAPACK64 = numpy.linalg._umath_linalg._ilp64
 
 _OLD_PROMOTION = lambda: np._get_promotion_state() == 'legacy'