bsd-user: Move PRAGMA_DISABLE_PACKED_WARNING etc to qemu.h

bsd-user: Move PRAGMA_DISABLE_PACKED_WARNING etc to qemu.h

For the moment, move PRAGMA_DISABLE_PACKED_WARNING and
PRAGMA_ENABLE_PACKED_WARNING back to bsd-user/qemu.h.

Of course, these should be in compiler.h, but that interferes with too
many things at the moment, so take one step back to unbreak clang
linux-user builds first. Use the exact same version that's in
linux-user/qemu.h since that's what should be in compiler.h.

Signed-off-by: Warner Losh <imp@bsdimp.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>