Restore missing #if

Signed-off-by: Dave Rodgman <dave.rodgman@arm.com>
diff --git a/library/aes.c b/library/aes.c
index dd803fe..85de815 100644
--- a/library/aes.c
+++ b/library/aes.c
@@ -42,6 +42,7 @@
 #endif
 #endif
 
+#if defined(MBEDTLS_ARCH_IS_X86)
 #if defined(MBEDTLS_PADLOCK_C)
 #if !defined(MBEDTLS_HAVE_ASM)
 #error "MBEDTLS_PADLOCK_C defined, but not all prerequisites"