was removed in 160b1697,
but is still needed when compiling with clang

This allows to refactor all those
```if(foo) {
throw bla;
}
```
blocks into ```DUNE_THROW_IF(foo, bla, "")```

dailywork-ftschindler

Introduced in 95f7ca2c1a5e4e638187e51491ec75837a2b7e2a, otherwise
we get linker errors with clang.

[fmatrix] add custom invert function 

- mainly copies the invert function from dune-common, except that the
LU decomposition always performs pivoting, not only if the diagonal entry
is below a threshold. This fixes the matrix inversion test for FieldMatrix
in dune-xt-la.

[cmake] add a 'license' target

which executes pylicense with all configs matching
"PROJECT_ROOT/.pylicense*.cfg"

[config.h.cmake] silence warning if FASP is not available

This reverts commit 2621d88d.
because cmake doesn't actually accept this despite what
the docs say

dailywork-ftschindler