Fix two more issues with r465416.

• Force build of a cross-compiler by defining CROSS_DIRECTORY_STRUCTURE in CFLAGS even if the build host matches the build target. This fixes such a cross compiler to not include /usr/local/lib in its default library path (e.g. amd64-gcc when built on amd64).
• Don't remove the include-fixed headers for the aarch64-none-elf-gcc and arm-none-eabi-gcc packages.
• Bump PORTREVISION.

Reported by: kevans (2)
Reviewed by: bdrewery, kevans
Differential Revision: https://reviews.freebsd.org/D14925