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]);
                                                               ^~~~~~~~~~~~

src/basic/fd-util.c

@@ -70,7 +70,7 @@ int safe_close(int fd) {
         return -1;
 }
 
-void safe_close_pair(int p[]) {
+void safe_close_pair(int p[static 2]) {
         assert(p);
 
         if (p[0] == p[1]) {

src/basic/fd-util.h

@@ -14,7 +14,7 @@
 
 int close_nointr(int fd);
 int safe_close(int fd);
-void safe_close_pair(int p[]);
+void safe_close_pair(int p[static 2]);
 
 static inline int safe_close_above_stdio(int fd) {
         if (fd < 3) /* Don't close stdin/stdout/stderr, but still invalidate the fd by returning -1 */

src/basic/siphash24.c

@@ -48,7 +48,7 @@ static inline void sipround(struct siphash *state) {
         state->v2 = rotate_left(state->v2, 32);
 }
 
-void siphash24_init(struct siphash *state, const uint8_t k[16]) {
+void siphash24_init(struct siphash *state, const uint8_t k[static 16]) {
         uint64_t k0, k1;
 
         assert(state);
@@ -187,7 +187,7 @@ uint64_t siphash24_finalize(struct siphash *state) {
         return state->v0 ^ state->v1 ^ state->v2  ^ state->v3;
 }
 
-uint64_t siphash24(const void *in, size_t inlen, const uint8_t k[16]) {
+uint64_t siphash24(const void *in, size_t inlen, const uint8_t k[static 16]) {
         struct siphash state;
 
         assert(in);

src/basic/siphash24.h

@@ -15,14 +15,14 @@ struct siphash {
         size_t inlen;
 };
 
-void siphash24_init(struct siphash *state, const uint8_t k[16]);
+void siphash24_init(struct siphash *state, const uint8_t k[static 16]);
 void siphash24_compress(const void *in, size_t inlen, struct siphash *state);
 #define siphash24_compress_byte(byte, state) siphash24_compress((const uint8_t[]) { (byte) }, 1, (state))
 
 uint64_t siphash24_finalize(struct siphash *state);
 
-uint64_t siphash24(const void *in, size_t inlen, const uint8_t k[16]);
+uint64_t siphash24(const void *in, size_t inlen, const uint8_t k[static 16]);
 
-static inline uint64_t siphash24_string(const char *s, const uint8_t k[16]) {
+static inline uint64_t siphash24_string(const char *s, const uint8_t k[static 16]) {
         return siphash24(s, strlen(s) + 1, k);
 }

src/basic/string-util.c

@@ -742,7 +742,7 @@ char *strreplace(const char *text, const char *old_string, const char *new_strin
         return ret;
 }
 
-static void advance_offsets(ssize_t diff, size_t offsets[2], size_t shift[2], size_t size) {
+static void advance_offsets(ssize_t diff, size_t offsets[static 2], size_t shift[static 2], size_t size) {
         if (!offsets)
                 return;