Fix compiler warnings on Windows in CopyFile.c

direct.h declares _mkdir() on Windows.

Prevent future compiler warnings with -Wall and -Werror.

Bug: 26355209
Test: `mmma -j30 build/libs/host` for aosp_arm64-eng is successful.

Change-Id: I6d6e4edca98bef57d62829e9d1ef4e2a96cdad3d

libs/host/Android.mk

@@ -4,6 +4,7 @@ include $(CLEAR_VARS)
 LOCAL_SRC_FILES:= \
     CopyFile.c
 
+LOCAL_CFLAGS := -Werror -Wall
 LOCAL_CFLAGS_darwin += -DMACOSX_RSRC
 
 LOCAL_MODULE:= libhost

libs/host/CopyFile.c

@@ -25,6 +25,7 @@
 #include <assert.h>
 
 #if defined(_WIN32)
+#include <direct.h>  /* For _mkdir() */
 #  define mkdir(path,mode)   _mkdir(path)
 #  define S_ISLNK(s) 0
 #  define lstat stat