bugfix: add a macro guard for avx512 operation (facebookresearch#4539)

Summary:
### What to fix
There is a small bug in the faiss/utils/rabitq_simd.h that some avx512 only supported operation is not guarded by a corresponding macro. As a result, the compile will fail if the arch does not support avx512.

### What I did
I add the macro guard.

### What I checked
I have compiled locally.

This should be an easy fix.

Pull Request resolved: facebookresearch#4539

Reviewed By: mnorris11

Differential Revision: D80734590

Pulled By: junjieqi

fbshipit-source-id: 603b94f29931576330eee1a8d1dcb73164df47f2

Author: conanhujinming

faiss/utils/rabitq_simd.h

@@ -26,6 +26,7 @@ namespace faiss {
  *
  * @return Lookup table as __m512i register
  */
+#if defined(__AVX512F__)
 inline __m512i get_lookup_512() {
     return _mm512_set_epi8(
             /* f */ 4,
@@ -93,7 +94,8 @@ inline __m512i get_lookup_512() {
             /* 1 */ 1,
             /* 0 */ 0);
 }
-
+#endif
+#if defined(__AVX2__)
 /**
  * Returns the lookup table for AVX2 popcount operations.
  * This table is used for lookup-based popcount implementation.
@@ -135,7 +137,9 @@ inline __m256i get_lookup_256() {
             /* e */ 3,
             /* f */ 4);
 }
+#endif
 
+#if defined(__AVX512F__)
 /**
  * Performs lookup-based popcount on AVX512 registers.
  *
@@ -152,7 +156,8 @@ inline __m512i popcount_lookup_avx512(__m512i v_and) {
     const __m512i popcnt2 = _mm512_shuffle_epi8(lookup, hi);
     return _mm512_add_epi8(popcnt1, popcnt2);
 }
-
+#endif
+#if defined(__AVX2__)
 /**
  * Performs lookup-based popcount on AVX2 registers.
  *
@@ -170,6 +175,7 @@ inline __m256i popcount_lookup_avx2(__m256i v_and) {
     return _mm256_add_epi8(popcnt1, popcnt2);
 }
 #endif
+#endif
 
 #if defined(__AVX512F__) && defined(__AVX512VPOPCNTDQ__)