Description:
------------
In the latest snapshot, /main/main.c (line 234) defines a sendmail_path of "/usr/sbin/sendmail -t -i" even if compiling for Windows.  As a result, Internal Sendmail Support for Windows is ALWAYS disabled since /ext/standard/mail.c (line 204) uses this variable to determine whether to use the internal SMTP server or an external sendmail program.  Since a non-null default value exists, and is not possible to set sendmail_path to NULL (as opposed to the empty string) via php.ini mail always tries to use sendmail which results in a "The system cannot find the path specified." error.  Main.c needs to check PHP_WIN32 and set the default sendmail_path to NULL when building for Windows.

Reproduce code:
---------------
<?php
	mail('me@mydomain.com', 'Test', 'Test Message');
?>

[mail function]
; For Win32 only.
SMTP = localhost
smtp_port = 25

; For Win32 only.
sendmail_from = Admin@mydomain.com

; For Unix only.  You may supply arguments as well (default: "sendmail -t -i").
;sendmail_path =

Expected result:
----------------
Mail should be sent.

Actual result:
--------------
The system cannot find the path specified.