windows: clarify the need for invalidcontinue.obj

Git's source code wants to be able to close() the same file descriptor
multiple times, ignoring the error returned by the second call (and the
ones after that), or to access the osfhandle of an already-closed stdout,
among other things that the UCRT does not like.

Simply linking invalidcontinue.obj allows such usage without resorting to
Debug Assertions (or exiting with exit code 9 in Release Mode).

Let's add a note so we don't forget, as suggested by Jeff Hostetler.

See https://msdn.microsoft.com/en-us/library/ms235330.aspx for more
details.

Signed-off-by: Johannes Schindelin <[email protected]>

Author: dscho

config.mak.uname

@@ -392,6 +392,9 @@ ifeq ($(uname_S),Windows)
 		compat/win32/dirent.o compat/win32/fscache.o
 	COMPAT_CFLAGS = -D__USE_MINGW_ACCESS -DDETECT_MSYS_TTY -DNOGDI -DHAVE_STRING_H -Icompat -Icompat/regex -Icompat/win32 -DSTRIP_EXTENSION=\".exe\"
 	BASIC_LDFLAGS = -IGNORE:4217 -IGNORE:4049 -NOLOGO -SUBSYSTEM:CONSOLE
+	# invalidcontinue.obj allows Git's source code to close the same file
+	# handle twice, or to access the osfhandle of an already-closed stdout
+	# See https://msdn.microsoft.com/en-us/library/ms235330.aspx
 	EXTLIBS = user32.lib advapi32.lib shell32.lib wininet.lib ws2_32.lib invalidcontinue.obj kernel32.lib ntdll.lib
 	PTHREAD_LIBS =
 	lib =