Add compatibility with gcc <= 11

Implementations based off headers in GCC release 11.4.0.

Signed-off-by: Andrei Tatar <andrei@unikraft.io>
Reviewed-by: Maria Sfiraiala <maria.sfiraiala@gmail.com>
Reviewed-by: Radu Nichita <radunichita99@gmail.com>
Approved-by: Razvan Deaconescu <razvand@unikraft.io>
Tested-by: Unikraft CI <monkey@unikraft.io>
GitHub-Closes: #3

include-gcc/immintrin.h

@@ -100,11 +100,13 @@
 
 #include <avx512vp2intersectvlintrin.h>
 
+#if (__GNUC__ >= 12)
 #ifdef __SSE2__
 #include <avx512fp16intrin.h>
 
 #include <avx512fp16vlintrin.h>
 #endif
+#endif
 
 #include <shaintrin.h>
 
@@ -120,6 +122,7 @@
 
 #include <vpclmulqdqintrin.h>
 
+#if (__GNUC__ >= 12)
 #ifdef __SSE2__
 #include <avx512bf16vlintrin.h>
 
@@ -129,6 +132,7 @@
 #include <avxneconvertintrin.h>
 #endif
 #endif
+#endif
 
 #include <amxtileintrin.h>