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/akcipher.c b/crypto/akcipher.c
index def301e..cfbdb06 100644
--- a/crypto/akcipher.c
+++ b/crypto/akcipher.c
@@ -17,6 +17,7 @@
 #include <linux/slab.h>
 #include <linux/string.h>
 #include <linux/crypto.h>
+#include <linux/compiler.h>
 #include <crypto/algapi.h>
 #include <linux/cryptouser.h>
 #include <net/netlink.h>
@@ -47,7 +48,7 @@ static int crypto_akcipher_report(struct sk_buff *skb, struct crypto_alg *alg)
 #endif
 
 static void crypto_akcipher_show(struct seq_file *m, struct crypto_alg *alg)
-	__attribute__ ((unused));
+	__maybe_unused;
 
 static void crypto_akcipher_show(struct seq_file *m, struct crypto_alg *alg)
 {