Problem: MS-Windows: startup code can be improved
Solution: Re-work and optimize win32 startup code
(Ken Takata)
* Revise the code and reduce #ifdefs.
* For VIMDLL, stop using the default CRT startup code to reduce the file
size.
The file size becomes ~130 KB -> ~34 KB on MSVC.
* Update comments. Make them consistent between os_w32dll.c and
os_w32exe.c.
closes: #15352
Signed-off-by: Ken Takata <kentkt@csc.jp>
Signed-off-by: Christian Brabandt <cb@256bit.org>