bug#42095: 28.0.50; Build fails on Windows/MinGW64

[Bruno Haible]

> > do we have any tests in our test suite to test the getrandom
> > function?
>
> No. Contributions would be welcome, I assume. Testing randomness is 
> nontrivial,
> though.

Maybe Emacs has no unit test for getrandom(), but gnulib has:

https://git.savannah.gnu.org/gitweb/?p=gnulib.git;a=blob;f=tests/test-getrandom.c;h=0e9fbb0c26b9f54087be4cf7371b0488dba59f4e;hb=HEAD

It does not really check randomness. It only verifies that different calls
produce different results.

If someone wants to provide such tests, I recall that Knuth's TAOCP II
contains the mathematical foundations of such analysis.

Bruno