Address MISRA C:2012 Rule 8.4

[Nicola Vetrini <nicola.vetrini@bugseng.com>]

The headline of Rule 8.4 is as follows:
"A compatible declaration shall be visible when an object or
function with external linkage is defined".

Some functions reported in [1][2] are lacking a declaration in the 
respective header files;
as remarked on xen-devel's IRC channel, this is ok since they are only 
called from asm code (e.g., start_xen). A similar discussion
had taken place in the past (see [3]) and the general consensus was to 
deviate these cases.
If that is still the case, a suitable project-wide deviation can be 
added to address these violations.

[1] 
https://saas.eclairit.com:3787/fs/var/local/eclair/XEN.ecdf/ECLAIR_normal/origin/staging/ARM64-Set1/210/PROJECT.ecd;/by_service/MC3R1.R8.4.html
[2] 
https://saas.eclairit.com:3787/fs/var/local/eclair/XEN.ecdf/ECLAIR_normal/origin/staging/X86_64-Set1/210/PROJECT.ecd;/by_service/MC3R1.R8.4.html
[3] 
https://lore.kernel.org/all/20220705210218.483854-2-burzalodowa@gmail.com/

Regards,

-- 
Nicola Vetrini, BSc
Software Engineer, BUGSENG srl (https://bugseng.com)