[PATCH v2 0/5] Improvements to the use of __attribute__((packed))

[Andrew Cooper <andrew.cooper3@citrix.com>]

Due to a lack of suitable define in scope, mce-apei.c ends up accidentally
creating a global unreferenced struct of type 'cper_mce_record', named
'__packed'.

This series is a cleanup of all use of __attribute__((packed)) in Xen.  A
formal define is created in compiler.h, all opencoded uses of the attribute
are updated to use the new define and the position of __packed is standardised
at the beginning of the struct rather than the end, so a lack of __packed in
scope will result in a compile error.

Patch 1 makes all the changes which have a material effect on Xen.

Patches 2 through 5 provide no functional change, but provide consistency with
the use of __attribute__((packed)) across the code.  They can be verified as
noops by diffing the resulting xen-syms.

This is compile tested on each architecture and functionally tested on x86.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>