cross-build: Define __*int*_t and include sys/cdefs.h

FreeBSD assumes that sys/types.h includes sys/cdefs.h, so add it here.
FreeBSD also needs __*int*_t defined for software we bootstrap (a lot of
it). GLIBC defines these, but musl does not, so we have to define them
here, even though it looks backwards. There's no good #define to key off
of, so use !defined GLIBC since on Linux defacto there's only two libc
implementations.

Co-authored-by: Val Packett <val@packett.cool>
Sponsored by: Netflix
Pull Request: https://github.com/freebsd/freebsd-src/pull/1066
Reviewed by: val_packett.cool
Differential Revision: https://reviews.freebsd.org/D45354