cross-build: Include sys/types.h from sys/param.h

FreeBSD has a style(9) enforced assumption that sys/param.h includes
sys/types.h. However, Linux under musl doesn't do this so go ahead and
explicitly include it here. It won't hurt on the glibc systems, and
helps musl.

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/D45352

Remove $FreeBSD$: two-line .h pattern

Remove /^\s*\*\n \*\s+\$FreeBSD\$$\n/

cross-build: fix some redeclaration warnings during bootstrap

MFC after: 3 days

Add Linux/macOS compatibility system headers to tools/build/cross-build

These headers are required in order to build the bootstrap tools on macOS
and Linux. A follow-up commit will add implementations of functions that
don't exist on those operating systems to -legacy when bootstrapping.

Reviewed By: brooks
Differential Revision: https://reviews.freebsd.org/D14316