BLD: fix some issues with undeclared internal build dependencies

This is a follow-up to scipygh-21983, and fixes some more issues reported
on scipygh-18909. It's possible to run into these when building with
a high level of parallelism, or trying to build just a single
target like `spatial/_qhull.so` with Ninja.

Author: rgommers

scipy/linalg/meson.build

@@ -28,6 +28,7 @@ cython_linalg = custom_target('cython_linalg',
   install_tag: 'devel'
 )
 cython_blas_pxd = cython_linalg[2]
+cython_lapack_pxd = cython_linalg[3]
 
 # pyx -> c, pyx -> cpp generators, depending on __init__.py here.
 linalg_init_cython_gen = generator(cython,
@@ -39,7 +40,7 @@ linalg_init_cython_gen = generator(cython,
 linalg_init_utils_cython_gen = generator(cython,
   arguments : cython_args,
   output : '@[email protected]',
-  depends : [_cython_tree, __init__py, _cy_array_utils_pxd])
+  depends : [_cython_tree, __init__py, _cy_array_utils_pxd, cython_lapack_pxd])
 
 # pyx -> c, pyx -> cpp generators, depending on copied pxd files and init
 linalg_cython_gen = generator(cython,
@@ -104,7 +105,7 @@ py3.extension_module('_flapack',
 
 # _decomp_interpolative
 py3.extension_module('_decomp_interpolative',
-  linalg_init_cython_gen.process('_decomp_interpolative.pyx'),
+  linalg_cython_gen.process('_decomp_interpolative.pyx'),
   c_args: cython_c_args,
   dependencies: np_dep,
   link_args: version_link_args,

scipy/spatial/meson.build

@@ -8,7 +8,7 @@ _spatial_pxd = [
 spt_cython_gen = generator(cython,
   arguments : cython_args,
   output : '@[email protected]',
-  depends : [_cython_tree, _spatial_pxd, _lib_pxd])
+  depends : [_cython_tree, _spatial_pxd, _lib_pxd, cython_lapack_pxd])
 
 qhull_src = [
   'qhull_src/src/geom2_r.c',