misra: consider conversion from UL or (void*) to function pointer as safe

Rule 11.1 states as following: "Conversions shall not be performed
between a pointer to a function and any other type."

This deviation from Rule 11.1 relies on both ABI definitions and compiler
implementations supported by Xen. The System V x86_64 ABI and the AArch64
ELF ABI define consistent and compatible representations (i.e., having
the same size and memory layout) for (void *), unsigned long, and function
pointers, enabling safe conversions between these types without data loss
or corruption. Additionally, GCC and Clang, faithfully implement the ABI
specifications, ensuring that the generated machine code conforms to these
guarantees. Developers must note that this behavior is not universal and
depends on platform-specific ABIs and compiler implementations.

Configure Eclair to avoid reporting violations for conversions from
unsigned long or (void *) to a function pointer.

Add a compile-time assertion into the file 'xen/common/version.c' to
confirm this conversion compatibility across X86 and ARM platforms
(assuming this file is common for them).

References:
- System V x86_64 ABI: https://gitlab.com/x86-psABIs/x86-64-ABI/-/jobs/artifacts/master/raw/x86-64-ABI/abi.pdf?job=build
- AArch64 ELF ABI: https://github.com/ARM-software/abi-aa/releases
- GCC: https://gcc.gnu.org/onlinedocs/gcc/ARM-Options.html
- Clang: https://clang.llvm.org/docs/CrossCompilation.html

Signed-off-by: Dmytro Prokopchuk <dmytro_prokopchuk1@epam.com>
Reviewed-by: Nicola Vetrini <nicola.vetrini@bugseng.com>
[stefano: remove special powerpc check]
Signed-off-by: Stefano Stabellini <stefano.stabellini@amd.com>
Acked-by: Stefano Stabellini <sstabellini@kernel.org>

automation/eclair_analysis/ECLAIR/deviations.ecl

@@ -375,6 +375,14 @@ constant expressions are required.\""
 }
 -doc_end
 
+-doc_begin="Conversion from unsigned long or (void *) to a function pointer can restore full information, provided that the source type has enough bits to restore it."
+-config=MC3A2.R11.1,casts+={safe,
+  "from(type(canonical(builtin(unsigned long)||pointer(builtin(void)))))
+   &&to(type(canonical(__function_pointer_types)))
+   &&relation(definitely_preserves_value)"
+}
+-doc_end
+
 -doc_begin="The conversion from a function pointer to a boolean has a well-known semantics that do not lead to unexpected behaviour."
 -config=MC3A2.R11.1,casts+={safe,
   "from(type(canonical(__function_pointer_types)))