Add jv_mem_strdup*() and callocs too

jv_alloc.h

@@ -17,6 +17,10 @@ static void jv_mem_invalidate(void* mem, size_t n) {
 
 void* jv_mem_alloc(size_t);
 void* jv_mem_alloc_unguarded(size_t);
+void* jv_mem_calloc(size_t, size_t);
+void* jv_mem_calloc_unguarded(size_t, size_t);
+char* jv_mem_strdup(const char *);
+char* jv_mem_strdup_unguarded(const char *);
 void jv_mem_free(void*);
 __attribute__((warn_unused_result)) void* jv_mem_realloc(void*, size_t);