add libc primitives to reduce dependencies

include/mimalloc/internal.h

@@ -189,7 +189,10 @@ bool        _mi_free_delayed_block(mi_block_t* block);
 void        _mi_free_generic(const mi_segment_t* segment, mi_page_t* page, bool is_local, void* p) mi_attr_noexcept;  // for runtime integration
 void        _mi_padding_shrink(const mi_page_t* page, const mi_block_t* block, const size_t min_size);
 
-// libc.c, c primitives
+// "libc.c"
+#include    <stdarg.h>
+void        _mi_vsnprintf(char* buf, size_t bufsize, const char* fmt, va_list args);
+void        _mi_snprintf(char* buf, size_t buflen, const char* fmt, ...);
 char        _mi_toupper(char c);
 int         _mi_strnicmp(const char* s, const char* t, size_t n);
 void        _mi_strlcpy(char* dest, const char* src, size_t dest_size);