py/emitglue: Fix macro logic that selects cache flushing code.

This fixes a regression made by 9e9da6c.

There are two issues here:

1. `MPY_FEATURE_ARCH` and `MP_NATIVE_ARCH_xxx` are not visible in this file
   because `py/persistentcode.h` is not included.

2. Even if they were visible the macro logic will not work because
   `MP_NATIVE_ARCH_xxx` are enum values and cannot be used in #if logic.

What this means is that the first #if is always true, so there is no cache
flushing on ARM (non-Thumb) or RISC-V targets.  This breaks native code on,
eg, ESP32-P4.

The fix here aims to simplify the logic by using built-in compiler defines
to select the target:

- On an ARM Thumb target with `__ICACHE_PRESENT` enabled, it will flush the
  cache.

- On an ARM (non-Thumb) target, it will prefer `__builtin___clear_cache()`
  if possible, otherwise it will use inline assembler.

- On a RISC-V target, it will use `MP_HAL_CLEAN_DCACHE()` if that macro is
  defined (that's only on ESP32-P4 at the moment).

The logic should be the same as before, except for the cases where an
emitter is enabled on a mismatching architecture.  For example, if
`MICROPY_EMIT_THUMB` and/or `MICROPY_EMIT_INLINE_THUMB` were enabled on a
non-Thumb target, previously that will try to generate code to flush caches
(which doesn't really make sense), but now it will not.  This actually
happened for `mpy-cross` which does enable all the emitters, and prior to
this fix would follow the Thumb path, but not generate any code because
`__ICACHE_PRESENT` is disabled (at least when building `mpy-cross` on x86).

Signed-off-by: Damien George <damien@micropython.org>

Author: dpgeorge

py/emitglue.c

@@ -107,17 +107,17 @@ void mp_emit_glue_assign_native(mp_raw_code_t *rc, mp_raw_code_kind_t kind, cons
     // Some architectures require flushing/invalidation of the I/D caches,
     // so that the generated native code which was created in data RAM will
     // be available for execution from instruction RAM.
-    #if MICROPY_EMIT_THUMB || MICROPY_EMIT_INLINE_THUMB || (MP_NATIVE_ARCH_ARMV6M <= MPY_FEATURE_ARCH && MPY_FEATURE_ARCH <= MP_NATIVE_ARCH_ARMV7EMDP)
+    #if defined(__thumb__) || defined(__thumb2__)
     #if __ICACHE_PRESENT == 1
     // Flush D-cache, so the code emitted is stored in RAM.
     MP_HAL_CLEAN_DCACHE(fun_data, fun_len);
     // Invalidate I-cache, so the newly-created code is reloaded from RAM.
     SCB_InvalidateICache();
     #endif
-    #elif MICROPY_EMIT_ARM || (MPY_FEATURE_ARCH == MP_NATIVE_ARCH_ARMV6)
+    #elif defined(__arm__)
     #if (defined(__linux__) && defined(__GNUC__)) || __ARM_ARCH == 7
     __builtin___clear_cache((void *)fun_data, (char *)fun_data + fun_len);
-    #elif defined(__arm__)
+    #else
     // Flush I-cache and D-cache.
     asm volatile (
         "0:"
@@ -127,7 +127,7 @@ void mp_emit_glue_assign_native(mp_raw_code_t *rc, mp_raw_code_kind_t kind, cons
         "mcr p15, 0, r0, c7, c7, 0\n" // invalidate I-cache and D-cache
         : : : "r0", "cc");
     #endif
-    #elif (MICROPY_EMIT_RV32 || MICROPY_EMIT_INLINE_RV32 || (MPY_FEATURE_ARCH == MP_NATIVE_ARCH_RV32IMC)) && defined(MP_HAL_CLEAN_DCACHE)
+    #elif defined(__riscv) && defined(MP_HAL_CLEAN_DCACHE)
     // Flush the D-cache.
     MP_HAL_CLEAN_DCACHE(fun_data, fun_len);
     #endif