scalapack: Fix exception when MKLROOT is unset

Fix `scalapack.MKLPkgConfigDependency` not to crash when `MKLROOT`
is unset:

```
  File "/meson/mesonbuild/dependencies/scalapack.py", line 65, in __init__
    super().__init__(name, env, kwargs, language=language)
    ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/meson/mesonbuild/dependencies/pkgconfig.py", line 322, in __init__
    self._set_cargs()
    ~~~~~~~~~~~~~~~^^
  File "/meson/mesonbuild/dependencies/scalapack.py", line 141, in _set_cargs
    cflags = self.pkgconfig.cflags(self.name, allow_system, define_variable=(('prefix', self.__mklroot.as_posix()),))
                                                                                        ^^^^^^^^^^^^^^^^^^^^^^^
AttributeError: 'NoneType' object has no attribute 'as_posix'
```

The code is crashing because the `_set_cargs()` method assumes that
`self.__mklroot` will always be set, presumably because it assumes
it will only be called only when `MKLPkgConfigDependency.__init__()`
finishes with `is_found = True`.  However, both `_set_cargs()`
and `_set_libs()` are called during `PkgConfigDependency.__init__()`,
and therefore they will be called if pkg-config lookup succeeds even
without `MKL_ROOT` set.

To avoid the issue, check for `self.__mklroot is None` in both
functions, and raise a `DependencyException` — effectively causing
the pkg-config lookup to fail in a natural way.

Fixes #11172

Signed-off-by: Michał Górny <mgorny@quansight.com>

0 files changed, 0 insertions, 0 deletions