Make pthread optional

Signed-off-by: Slendi <slendi@socopon.com>

src/dcfg.c

@@ -11,7 +11,18 @@
 #include <stdlib.h>
 #include <string.h>
 
+#ifdef DCFG_PTHREAD_SUPPORT
 #include <pthread.h>
+#else
+typedef struct {
+  int unused;
+} pthread_mutex_t;
+
+void pthread_mutex_init(pthread_mutex_t *, void *);
+void pthread_mutex_destroy(pthread_mutex_t *);
+void pthread_mutex_lock(pthread_mutex_t *);
+void pthread_mutex_unlock(pthread_mutex_t *);
+#endif
 
 int64_t dcfg_strtoll(const char *s, char **end, int base) {
   size_t n = strlen(s);