Previously, this environment variable was set in the pager_preexec
callback, which is conditionally-compiled only on Unix, because it is not,
and cannot be, called on Windows.
With this patch the env member of struct child_process is used to set
the environment variable, which also works on Windows.
Noticed by Alexey Borzenkov.
Signed-off-by: Johannes Sixt <j6t@kdbg.org> Signed-off-by: Junio C Hamano <gitster@pobox.com>