Relicense findprog-in under LGPLv2+

[Bruno Haible]

Hi Paul,

I would like to relicense the module 'findprog-in' under LGPLv2+, so that
I can use it for the native Windows implementation of the modules 'posix_spawn'
and 'posix_spawnp' — which are under LGPLv2+.

This module has one contribution from you:
https://lists.gnu.org/archive/html/bug-gnulib/2019-09/msg00062.html

Would you approve this license change for this contribution?

(Of course the dependency to the 'xalloc' module will then also go away,
and be replaced with an error return with errno = ENOMEM.)

Bruno