crypto: Replaced gcc specific attributes with macros from compiler.h

Continuing from this commit: 52f5684c8e1e
("kernel: use macros from compiler.h instead of __attribute__((...))")

I submitted 4 total patches. They are part of task I've taken up to
increase compiler portability in the kernel. I've cleaned up the
subsystems under /kernel /mm /block and /security, this patch targets
/crypto.

There is <linux/compiler.h> which provides macros for various gcc specific
constructs. Eg: __weak for __attribute__((weak)). I've cleaned all
instances of gcc specific attributes with the right macros for the crypto
subsystem.

I had to make one additional change into compiler-gcc.h for the case when
one wants to use this: __attribute__((aligned) and not specify an alignment
factor. From the gcc docs, this will result in the largest alignment for
that data type on the target machine so I've named the macro
__aligned_largest. Please advise if another name is more appropriate.

Signed-off-by: Gideon Israel Dsouza <gidisrael@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
diff --git a/crypto/skcipher.c b/crypto/skcipher.c
index 6ee6a15..014af74 100644
--- a/crypto/skcipher.c
+++ b/crypto/skcipher.c
@@ -19,6 +19,7 @@
 #include <crypto/scatterwalk.h>
 #include <linux/bug.h>
 #include <linux/cryptouser.h>
+#include <linux/compiler.h>
 #include <linux/list.h>
 #include <linux/module.h>
 #include <linux/rtnetlink.h>
@@ -807,7 +808,7 @@ static void crypto_skcipher_free_instance(struct crypto_instance *inst)
 }
 
 static void crypto_skcipher_show(struct seq_file *m, struct crypto_alg *alg)
-	__attribute__ ((unused));
+	__maybe_unused;
 static void crypto_skcipher_show(struct seq_file *m, struct crypto_alg *alg)
 {
 	struct skcipher_alg *skcipher = container_of(alg, struct skcipher_alg,