win32: Add missing header files for nginx compilation

From: Vlad Vissoultchev
    Date: Tue, 12 Apr 2016 21:02:43 +0300
    Subject: win32: Add missing header files for nginx compilation

    The new ones are hoisted from mingw-w64 as most other headers under
    `win32/include/winapi`

win32/include/_mingw.h

@@ -133,4 +133,8 @@ typedef struct localeinfo_struct _locale_tstruct,*_locale_t;
 # define _WIN32_WINNT 0x502
 #endif
 
+#define __C89_NAMELESS
+#define __MINGW_EXTENSION
+#define WINAPI_FAMILY_PARTITION(X) 1
+
 #endif /* __MINGW_H */