Fix Clang compiler warnings

When building using a newer Clang with additional diagnostics
the following warnings are given:
 -Wunused-but-set-variable
 -Wstrict-prototypes
These issues are corrected in this commit.

Reproducable using:
CC="clang-13" CFLAGS="-Wall -pedantic" cmake ..

src/slug.c

@@ -90,7 +90,6 @@ int r3_slug_parse(r3_slug_t *s, const char *needle, int needle_len, const char *
         return 0;
     }
 
-    int cnt = 0;
     int state = 0;
     const char * p = offset;
 
@@ -122,7 +121,6 @@ int r3_slug_parse(r3_slug_t *s, const char *needle, int needle_len, const char *
             if (s->pattern) {
                 s->pattern_len = p - s->pattern;
             }
-            cnt++;
             state--;
             p++;
             break;

tests/bench.c

@@ -17,15 +17,15 @@
 
 
 
-unsigned long unixtime() {
+unsigned long unixtime(void) {
     struct timeval tp;
     if (gettimeofday((struct timeval *) &tp, (NULL)) == 0) {
         return tp.tv_sec;
     }
     return 0;
 }
 
-double microtime() {
+double microtime(void) {
     struct timeval tp;
     long sec = 0L;
     double msec = 0.0;
@@ -93,7 +93,7 @@ void bench_append_csv(char *filename, int countOfB, ...) {
 
 
 
-int main()
+int main(void)
 {
     R3Node * n = r3_tree_create(1);
 

tests/bench.h

@@ -22,9 +22,9 @@ typedef struct {
     double end;
 } bench;
 
-unsigned long unixtime();
+unsigned long unixtime(void);
 
-double microtime();
+double microtime(void);
 
 void bench_start(bench *b);
 

tests/check_tree.c

@@ -304,7 +304,7 @@ START_TEST (test_node_construct_and_free)
 }
 END_TEST
 
-static R3Node * create_simple_str_tree() {
+static R3Node * create_simple_str_tree(void) {
     R3Node * n;
     n = r3_tree_create(10);
     r3_tree_insert_path(n, "/zoo", NULL);