scripts/nsis.py: Automatically package required DLLs of QEMU executables

scripts/nsis.py: Automatically package required DLLs of QEMU executables

At present packaging the required DLLs of QEMU executables is a
manual process, and error prone.

Actually build/config-host.mak contains a GLIB_BINDIR variable
which is the directory where glib and other DLLs reside. This
works for both Windows native build and cross-build on Linux.
We can use it as the search directory for DLLs and automate
the whole DLL packaging process.

Signed-off-by: Bin Meng <bin.meng@windriver.com>
Message-Id: <20220908132817.1831008-4-bmeng.cn@gmail.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Tested-by: Stefan Weil <sw@weilnetz.de>
Signed-off-by: Stefan Weil <sw@weilnetz.de>