[breaking change] PTRACE_GETFPXREGS and PTRACE_SETFPXREGS were incorrectly re-exported on arm but they are x86 specific

fd_set isn't automatically copyable. While it will be possible to fix
that, for now just remove these so that they don't block other changes.

dirent contains a flexible array member, so don't test its sizeof, don't
allow it to be copied, and don't represent it with an artificial size.

Also, locale_t is a typedef for a pointer to an opaque struct, so
represent it that way explicitly.

Rustc is changing it to be target_os; for now, recognize both.

defined for 32-bit Solarish targets.  Since rust doesn't currently
support 32-bit Solarish targets, the line is both unnecessary and wrong.

Added recently and will be used in libstd!