Issue created by Wayne Thornton:
https://gitlab.rtems.org/rtems/rtos/rtems/-/work_items/5647
## Description:
We have introduced a new Super Core architecture hook, `_CPU_Spin_wait()`, to
mitigate aggressive speculative execution penalties, reduce thermal load, and
lower bus contention during SMP spin-wait polling loops. The reference template
is currently documented in `cpukit/score/cpu/no_cpu/include/rtems/score/cpu.h`
and natively implemented for `x86_64` upon merging of rtems/rtos/rtems!1256.
The i386 architecture port needs to mirror the `x86_64` behavior by
implementing the pipeline pause instruction in
`cpukit/score/cpu/i386/include/rtems/score/cpu.h`.
Suggested Implementation:
This should utilize the standard x86 pause instruction (historically encoded as
`rep; nop,` which executes safely as a standard no-op on legacy IA-32
processors prior to the Pentium 4 / SSE2):
```
static inline void _CPU_Spin_wait( void )
{
__asm__ volatile( "pause" ::: "memory" );
}
#define _CPU_Spin_wait _CPU_Spin_wait
```
## Verification:
Validate that the implementation compiles cleanly on SMP i386 targets and
passes the standalone SMP spin-wait test suite:
`testsuites/smptests/smpspinwait01`. Once defined, the preprocessor will
automatically override the temporary test-level fallback in `init.c`.
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