ipxfrm: use alloca to allocate stack space

Clang doesn't support the gcc extension for embeddeding flexible arrays
inside of structures.  Use the slightly more portable alloca().
Signed-off-by: Mike Frysinger <vapier@gentoo.org>

ip/ipxfrm.c

@@ -25,6 +25,7 @@
  *	Masahide NAKAMURA @USAGI
  */
 
+#include <alloca.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -555,16 +556,13 @@ static inline void xfrm_algo_print(struct xfrm_algo *algo, int type, int len,
 static void xfrm_aead_print(struct xfrm_algo_aead *algo, int len,
 			    FILE *fp, const char *prefix)
 {
-	struct {
-		struct xfrm_algo algo;
-		char key[algo->alg_key_len / 8];
-	} base;
+	struct xfrm_algo *base_algo = alloca(sizeof(*base_algo) + algo->alg_key_len / 8);
 
-	memcpy(base.algo.alg_name, algo->alg_name, sizeof(base.algo.alg_name));
-	base.algo.alg_key_len = algo->alg_key_len;
-	memcpy(base.algo.alg_key, algo->alg_key, algo->alg_key_len / 8);
+	memcpy(base_algo->alg_name, algo->alg_name, sizeof(base_algo->alg_name));
+	base_algo->alg_key_len = algo->alg_key_len;
+	memcpy(base_algo->alg_key, algo->alg_key, algo->alg_key_len / 8);
 
-	__xfrm_algo_print(&base.algo, XFRMA_ALG_AEAD, len, fp, prefix, 0);
+	__xfrm_algo_print(base_algo, XFRMA_ALG_AEAD, len, fp, prefix, 0);
 
 	fprintf(fp, " %d", algo->alg_icv_len);
 
@@ -574,16 +572,13 @@ static void xfrm_aead_print(struct xfrm_algo_aead *algo, int len,
 static void xfrm_auth_trunc_print(struct xfrm_algo_auth *algo, int len,
 				  FILE *fp, const char *prefix)
 {
-	struct {
-		struct xfrm_algo algo;
-		char key[algo->alg_key_len / 8];
-	} base;
+	struct xfrm_algo *base_algo = alloca(sizeof(*base_algo) + algo->alg_key_len / 8);
 
-	memcpy(base.algo.alg_name, algo->alg_name, sizeof(base.algo.alg_name));
-	base.algo.alg_key_len = algo->alg_key_len;
-	memcpy(base.algo.alg_key, algo->alg_key, algo->alg_key_len / 8);
+	memcpy(base_algo->alg_name, algo->alg_name, sizeof(base_algo->alg_name));
+	base_algo->alg_key_len = algo->alg_key_len;
+	memcpy(base_algo->alg_key, algo->alg_key, algo->alg_key_len / 8);
 
-	__xfrm_algo_print(&base.algo, XFRMA_ALG_AUTH_TRUNC, len, fp, prefix, 0);
+	__xfrm_algo_print(base_algo, XFRMA_ALG_AUTH_TRUNC, len, fp, prefix, 0);
 
 	fprintf(fp, " %d", algo->alg_trunc_len);