Define _GNU_SOURCE properly, other header fixes

This lets -std=c89 build for gcc 8.4.0

cli-authpubkey.c

@@ -125,7 +125,7 @@ void recv_msg_userauth_pk_ok() {
 static void cli_buf_put_sign(buffer* buf, sign_key *key, enum signature_type sigtype,
 			const buffer *data_buf) {
 #if DROPBEAR_CLI_AGENTFWD
-	// TODO: rsa-sha256 agent
+	/* TODO: rsa-sha256 agent */
 	if (key->source == SIGNKEY_SOURCE_AGENT) {
 		/* Format the agent signature ourselves, as buf_put_sign would. */
 		buffer *sigblob;

configure.ac

@@ -47,6 +47,9 @@ DB_TRYADDCFLAGS([-Wno-pointer-sign])
 AC_MSG_NOTICE([Checking if compiler '$CC' supports -fno-strict-overflow])
 DB_TRYADDCFLAGS([-fno-strict-overflow])
 
+# needed for various extensions. define early before autoconf tests
+AC_DEFINE([_GNU_SOURCE], [], [Use GNU extensions if glibc])
+
 STATIC=0
 AC_ARG_ENABLE(static,
 	[  --enable-static         Build static binaries],

dbmalloc.h

@@ -1,9 +1,9 @@
 #ifndef DBMALLOC_H_
 #define DBMALLOC_H_
 
-#include "stdint.h"
-#include "stdlib.h"
 #include "options.h"
+#include <stdint.h>
+#include <stdlib.h>
 
 void * m_malloc(size_t size);
 void * m_calloc(size_t nmemb, size_t size);

fuzz.h

@@ -80,7 +80,7 @@ struct dropbear_fuzz_options {
     int do_jmp;
     sigjmp_buf jmp;
 
-    // write out decrypted session data to this FD if it's set
+    // write out decrypted session data to this FD if it is set
     // flag - this needs to be set manually in cli-main.c etc
     int dumping;
     // the file descriptor
@@ -114,6 +114,6 @@ struct passwd* fuzz_getpwnam(const char *login);
 #define getpwuid(x) fuzz_getpwuid(x)
 #endif // FUZZ_NO_REPLACE_GETPW
 
-#endif // DROPBEAR_FUZZ
+#endif /* DROPBEAR_FUZZ */
 
 #endif /* DROPBEAR_FUZZ_H */

includes.h

@@ -25,9 +25,6 @@
 #ifndef DROPBEAR_INCLUDES_H_
 #define DROPBEAR_INCLUDES_H_
 
-/* uclibc needs _GNU_SOURCE, maybe other things? */
-#define _GNU_SOURCE
-
 #include "options.h"
 #include "debug.h"
 

svr-auth.c

@@ -25,7 +25,6 @@
 /* This file (auth.c) handles authentication requests, passing it to the
  * particular type (auth-passwd, auth-pubkey). */
 
-#include <limits.h>
 
 #include "includes.h"
 #include "dbutil.h"