patch 9.1.0621: MS-Windows: startup code can be improved

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>
diff --git a/src/Make_mvc.mak b/src/Make_mvc.mak
index adcf19a..c750311 100644
--- a/src/Make_mvc.mak
+++ b/src/Make_mvc.mak
@@ -1302,11 +1302,11 @@
 
 $(GVIM).exe: $(OUTDIR) $(EXEOBJG) $(VIMDLLBASE).dll
 	$(LINK) $(LINKARGS1) /subsystem:$(SUBSYSTEM) -out:$(GVIM).exe \
-		$(EXEOBJG) $(VIMDLLBASE).lib $(LIBC)
+		$(EXEOBJG) $(VIMDLLBASE).lib
 
 $(VIM).exe: $(OUTDIR) $(EXEOBJC) $(VIMDLLBASE).dll
 	$(LINK) $(LINKARGS1) /subsystem:$(SUBSYSTEM_CON) -out:$(VIM).exe \
-		$(EXEOBJC) $(VIMDLLBASE).lib $(LIBC)
+		$(EXEOBJC) $(VIMDLLBASE).lib
 
 !else
 
@@ -1715,10 +1715,10 @@
 $(OUTDIR)/os_w32exe.obj:	$(OUTDIR) os_w32exe.c  $(INCL)
 
 $(OUTDIR)/os_w32exec.obj:	$(OUTDIR) os_w32exe.c  $(INCL)
-	$(CC) $(CFLAGS:-DFEAT_GUI_MSWIN=) /Fo$@ os_w32exe.c
+	$(CC) $(CFLAGS:-DFEAT_GUI_MSWIN=) /DUSE_OWNSTARTUP /GS- /Fo$@ os_w32exe.c
 
 $(OUTDIR)/os_w32exeg.obj:	$(OUTDIR) os_w32exe.c  $(INCL)
-	$(CC) $(CFLAGS) /Fo$@ os_w32exe.c
+	$(CC) $(CFLAGS) /DUSE_OWNSTARTUP /GS- /Fo$@ os_w32exe.c
 
 $(OUTDIR)/pathdef.obj:	$(OUTDIR) $(PATHDEF_SRC) $(INCL)
 	$(CC) $(CFLAGS_OUTDIR) $(PATHDEF_SRC)