Fix mingw compiler error

src/civetweb.c

@@ -159,7 +159,9 @@ typedef long off_t;
 #define INT64_FMT  "I64d"
 
 #define WINCDECL __cdecl
+#define SHUT_RD 0
 #define SHUT_WR 1
+#define SHUT_BOTH 2
 #define snprintf _snprintf
 #define vsnprintf _vsnprintf
 #define access _access

src/main.c

@@ -50,7 +50,9 @@
 #include <shlobj.h>
 
 #define getcwd(a,b) _getcwd(a,b)
+#if !defined(__MINGW32__)
 extern char *_getcwd(char *buf, size_t size);
+#endif
 static int guard = 0;                   /* test if any dialog is already open */
 
 #ifndef PATH_MAX