res_crypto.c: Avoid using the non-portable ALLPERMS macro.

ALLPERMS is not POSIX and it's trivial enough to not jump through
autoconf hoops to check for it.

Fixes #149.

res/res_crypto.c

@@ -217,10 +217,15 @@ static struct ast_key *try_load_key(const char *dir, const char *fname, int ifd,
 		return NULL;
 	}
 
+	/* FILE_MODE_BITS is a bitwise OR of all possible file mode bits encoded in
+	 * the `st_mode` member of `struct stat`. For POSIX compatible systems this
+	 * will be 07777. */
+#define FILE_MODE_BITS (S_ISUID|S_ISGID|S_ISVTX|S_IRWXU|S_IRWXG|S_IRWXO)
+
 	/* only user read or read/write modes allowed */
 	if (ktype == AST_KEY_PRIVATE &&
-	    ((st.st_mode & ALLPERMS) & ~(S_IRUSR | S_IWUSR)) != 0) {
-		ast_log(LOG_ERROR, "Private key file has bad permissions: %s: %#4o\n", ffname, st.st_mode & ALLPERMS);
+	    ((st.st_mode & FILE_MODE_BITS) & ~(S_IRUSR | S_IWUSR)) != 0) {
+		ast_log(LOG_ERROR, "Private key file has bad permissions: %s: %#4o\n", ffname, st.st_mode & FILE_MODE_BITS);
 		fclose(f);
 		return NULL;
 	}