Add patch to fix definition of environ variable

Add patch to fix definition of environ variable

The patch properly defines `environ` as an array of pointers, the last
of which is NULL. In the previous definition, `environ` was NULL, which
is not OK. The definition is now replaced to an array of a single NULL
element.

Signed-off-by: Razvan Deaconescu <razvand@unikraft.io>
Reviewed-by: Stefan Jumarea <stefanjumarea02@gmail.com>
Approved-by: Simon Kuenzer <simon@unikraft.io>
Tested-by: Unikraft CI <monkey@unikraft.io>
GitHub-Closes: #30