build: rework x86 CPU variants

Type: improvement
Change-Id: Ief243f88e654e578ef9b8060fcf535b364aececb
Signed-off-by: Damjan Marion <damarion@cisco.com>
diff --git a/src/vppinfra/string.h b/src/vppinfra/string.h
index a3db926..3dafe89 100644
--- a/src/vppinfra/string.h
+++ b/src/vppinfra/string.h
@@ -71,7 +71,7 @@
  * so don't let it anywhere near them.
  */
 #ifndef __COVERITY__
-#if __AVX512F__
+#if __AVX512BITALG__
 #include <vppinfra/memcpy_avx512.h>
 #elif __AVX2__
 #include <vppinfra/memcpy_avx2.h>