tree-wide: use c99 static for array size declarations

https://hamberg.no/erlend/posts/2013-02-18-static-array-indices.html

This only works with clang, unfortunately gcc doesn't seem to implement the check
(tested with gcc-8.2.1-5.fc29.x86_64).

Simulated error:
[2/3] Compiling C object 'systemd-nspawn@exe/src_nspawn_nspawn.c.o'.
../src/nspawn/nspawn.c:3179:45: warning: array argument is too small; contains 15 elements, callee requires at least 16 [-Warray-bounds]
                        candidate = (uid_t) siphash24(arg_machine, strlen(arg_machine), hash_key);
                                            ^                                           ~~~~~~~~
../src/basic/siphash24.h:24:64: note: callee declares array parameter as static here
uint64_t siphash24(const void *in, size_t inlen, const uint8_t k[static 16]);
                                                               ^~~~~~~~~~~~

1 files changed, 1 insertions, 1 deletions

diff --git a/src/core/namespace.h b/src/core/namespace.h
index 1188c6d595..5e0ec97969 100644
--- a/src/core/namespace.h
+++ b/src/core/namespace.h
@@ -91,7 +91,7 @@ int setup_tmp_dirs(
                 char **tmp_dir,
                 char **var_tmp_dir);
 
-int setup_netns(int netns_storage_socket[2]);
+int setup_netns(int netns_storage_socket[static 2]);
 
 const char* protect_home_to_string(ProtectHome p) _const_;
 ProtectHome protect_home_from_string(const char *s) _pure_;