Protect polyfills to only be defined when their instruction set is av…

…ailable.

`_mm512_dpbusd_epi32_madd`'s implementation uses the following AVX512BW intrinsics:

- `_mm512_sub_epi8`
- `_mm512_maddubs_epi16`
- `_mm512_madd_epi16`

`_mm256_dpbusd_epi32_bw`'s implementation uses the following AVX2 intrinsics:

- `_mm256_srli_epi32`
- `_mm256_xor_si256`
- `_mm256_sub_epi8`
- `_mm256_maddubs_epi16`
- `_mm256_madd_epi16`
- `_mm256_add_epi32`

PiperOrigin-RevId: 657957490

src/xnnpack/intrinsics-polyfill.h

@@ -170,6 +170,7 @@ void _mm512_storeu_epi32 (void* mem_addr, __m512i a) {
 }
 #endif  // GCC pre-10
 
+#ifdef __AVX512BW__
 // VNNI replacement that uses vpmaddubsw.
 // u4 is uint4 in lower 4 bits.
 static XNN_INTRINSIC
@@ -181,9 +182,10 @@ __m512i _mm512_dpbusd_epi32_madd(__m512i i32, const __m512i u8, const __m512i u4
   const __m512i v = _mm512_madd_epi16(i12, vsixteen);  // convert 16 bits to 32 bits
   return _mm512_add_epi32(i32, v);
 }
+#endif  // __AVX512BW__
 #endif  // __AVX512F__
 
-#ifdef __AVX__
+#ifdef __AVX2__
 
 // AVXVNNI replacement that uses vpmaddubsw.
 // i4h is int4 in upper 4 bits.  Low bits are zero.
@@ -199,7 +201,7 @@ __m256i _mm256_dpbusd_epi32_bw(__m256i i32, const __m256i u8, const __m256i i4h)
   return _mm256_add_epi32(i32, v);
 }
 
-#endif  // __AVX__
+#endif  // __AVX2__
 
 
 #if XNN_ARCH_ARM