Improve C standard compliance.

- Don't cast between object and function pointers.
- Use standard compliant `__VA_ARGS__` in macros.
- Add explicit `__extension__` on unnamed union in struct (it's a GNU
  extension).
- Remove ; after function definitions.
- Replace `const T foo = 3;` for integral types `T` with `enum { foo = 3 };`.
  Folding integral constants like that as compile time constants is a GNU
  extension. Arrays allocated with `foo` as dimension are VLAs on strictly
  compliant C99 compilers.
- Replace empty initialiser list `{}` with zero-initialiser-list `{0}`.
  The former is a GNU extension meaning the latter.
- Cast `T*` (where `T != void`) to `void *` in format arguments. While any
  object pointer can be implicitly converted to and from `void *`, this
  conversion does not happen in variadic function calls.
- Replace arithmetic on `void *` with arithmetic on `char *`. The former
  is non-compliant.
- Replace non-`int`-derived types (like `uint16_t`, which is
  `short`-derived) in bit fields with `int`-derived types. Using any type
  other than `int` or `unsigned int` (or any of their aliases) in bit
  fields is a GNU extension.

3 files changed, 3 insertions, 3 deletions

diff --git a/testing/dns3_test.c b/testing/dns3_test.c
index 063ea8c7..830ecfd8 100644
--- a/testing/dns3_test.c
+++ b/testing/dns3_test.c
@@ -102,7 +102,7 @@ int main(int argc, char *argv[])
         return -1;
     }
 
-    uint8_t buffer[512] = {};
+    uint8_t buffer[512] = {0};
     int r_len = recv(sock, buffer, sizeof(buffer), 0);
 
     if (r_len < (int)p_len) {
diff --git a/testing/misc_tools.c b/testing/misc_tools.c
index de246d82..b667f991 100644
--- a/testing/misc_tools.c
+++ b/testing/misc_tools.c
@@ -85,4 +85,4 @@ int cmdline_parsefor_ipv46(int argc, char **argv, uint8_t *ipv6enabled)
     }
 
     return argvoffset;
-};
+}
diff --git a/testing/nTox.c b/testing/nTox.c
index ec6b152c..fcfbe004 100644
--- a/testing/nTox.c
+++ b/testing/nTox.c
@@ -57,7 +57,7 @@ uint8_t flag[HISTORY];
 char input_line[STRING_LENGTH];
 
 /* wrap: continuation mark */
-const size_t wrap_cont_len = 3;
+enum { wrap_cont_len = 3 };
 const char wrap_cont_str[] = "\n+ ";
 
 #define STRING_LENGTH_WRAPPED (STRING_LENGTH + 16 * (wrap_cont_len + 1))