Implemented the __sys_write() operation for *BSD (x86-64).
Implemented platform support for FreeBSD (x86-64).
Ensured that the OpenBSD ELF tag isn't used on other *BSDs.
Implemented platform support for Solaris (x86-64).

Solaris 11.2 on x86-64 requires: ./configure CC='gcc -std=c99 -m64'
Ensured that the 'restrict' keyword doesn't cause trouble.

Use of AC_C_RESTRICT should mean that it isn't necessary for CFLAGS
to explicitly contain -std=c99 or -std=c11. To be determined.