cross-build: Provide _PASSWORD_EFMT1 for libcrypt on Linux

Linux's pwd.h does not define _PASSWORD_EFMT1 (macOS's does), so we need
to define it in order to be able to bootstrap libcrypt (crypt-des.c uses
it) on non-FreeBSD, which will be done in a subsequent commit.

MFC after: 1 week

(cherry picked from commit e0cb1fe7dd34e9786320befa623b181d29d6bdf9)