diff -Naur Python-3.7.0-orig/setup.py Python-3.7.0/setup.py
--- Python-3.7.0-orig/setup.py	2018-07-12 10:22:07.080033900 +0300
+++ Python-3.7.0/setup.py	2018-07-12 10:22:12.368443200 +0300
@@ -39,6 +39,17 @@
     return sys.platform
 host_platform = get_platform()
 
+# On MSYS, os.system needs to be wrapped with sh.exe
+# as otherwise all the io redirection will fail.
+# Arguably, this could happen inside the real os.system
+# rather than this monkey patch.
+if sys.platform == "win32" and "MSYSTEM" in os.environ:
+    os_system = os.system
+    def msys_system(command):
+        command_in_sh = 'sh.exe -c "%s"' % command.replace("\\", "\\\\")
+        return os_system(command_in_sh)
+    os.system = msys_system
+
 # Were we compiled --with-pydebug or with #define Py_DEBUG?
 COMPILED_WITH_PYDEBUG = ('--with-pydebug' in sysconfig.get_config_var("CONFIG_ARGS"))