Back out the removal of custom version of endian.h system header.
On recent systems, it just falls back to <sys/endian.h>. But on
older systems like 5.0-DP1 or 4-STABLE, this private version may
be necessary, as crunchide(1) is a cross-tool for "make release".
Spotted by: kris, markm
longer includes machine/elf.h.
* consumers of elf.h now use the minimalist elf header possible.
This change is motivated by Binutils 2.11.0 and too much clashing over
our base elf headers and the Binutils elf headers.
