Avoid error from old gcc version

Signed-off-by: Dave Rodgman <dave.rodgman@arm.com>
diff --git a/library/platform_util.c b/library/platform_util.c
index cfd982e..09216ed 100644
--- a/library/platform_util.c
+++ b/library/platform_util.c
@@ -128,8 +128,9 @@
 #endif
 
 #if defined(__GNUC__)
-        /* For clang and gcc, pretend that we have some assembly that reads the
+        /* For clang and recent gcc, pretend that we have some assembly that reads the
          * zero'd memory as an additional protection against being optimised away. */
+#if defined(__clang__) || (__GNUC__ >= 10)
 #if defined(__clang__)
 #pragma clang diagnostic push
 #pragma clang diagnostic ignored "-Wvla"
@@ -144,6 +145,7 @@
 #pragma GCC diagnostic pop
 #endif
 #endif
+#endif
     }
 }
 #endif /* MBEDTLS_PLATFORM_ZEROIZE_ALT */