Ошибка при создании расширения Ruby в C

образец
⇒Исходный код(включая make-файл)

Я делаю тест для образца выше,
Но когда я компилирую, он получил ошибку!
Я сделал это неправильно?

H:\Ruby\test_ymal\MyTest>make
compiling MyTest.c
In file included from d:/RailsInstaller/Ruby2.2.0/include/ruby-2.2.0/ruby/define
from d:/RailsInstaller/Ruby2.2.0/include/ruby-2.2.0/ruby/ruby.h
from d:/RailsInstaller/Ruby2.2.0/include/ruby-2.2.0/ruby.h:33,
from MyTest.c:2:
d:/RailsInstaller/Ruby2.2.0/include/ruby-2.2.0/ruby/win32.h:319:44: warning: 'st
extern int clock_gettime(clockid_t, struct timespec *);
^
d:/RailsInstaller/Ruby2.2.0/include/ruby-2.2.0/ruby/win32.h:320:43: warning: 'st
extern int clock_getres(clockid_t, struct timespec *);
^
linking shared-object mytest.so
process_begin: CreateProcess(NULL, rm -f mytest.so, ...) failed.
make (e=2):
Makefile:253: recipe for target 'mytest.so' failed
make: [mytest.so] Error 2 (ignored)
c:/mingw/bin/../lib/gcc/mingw32/4.8.1/../../../../mingw32/bin/ld.exe: mytest-i38
mytest-i386-mingw32.def: file not recognized: File truncated
collect2.exe: error: ld returned 1 exit status
Makefile:253: recipe for target 'mytest.so' failed
make: *** [mytest.so] Error 1

—-добавить к 2016/05/03 ———————-

H:\Ruby\test_ymal\MyTest>make
generating mytest-i386-mingw32.def
compiling MyTest.c
linking shared-object mytest.so
process_begin: CreateProcess(NULL, rm -f mytest.so, ...) failed.
make (e=2):
Makefile:271: recipe for target 'mytest.so' failed
make: [mytest.so] Error 2 (ignored)

но файл (mytest.so), протестированный в ruby, в порядке.
как решить эту ошибку?
process_begin: не удалось создать CreateProcess (NULL, rm -f mytest.so, …)

irb(main):003:0> require 'H:\Ruby\test_ymal\MyTest\mytest.so'
=> true
irb(main):004:0> include MyTest
=> Object
irb(main):005:0> puts test1
10
=> nil
irb(main):006:0> exit