patch 8.0.0410: newer gettext/iconv library has extra dll file

Problem:    Newer gettext/iconv library has extra dll file.
Solution:   Add the file to the Makefile and nsis script. (Christian Brabandt)
diff --git a/nsis/gvim.nsi b/nsis/gvim.nsi
index 26d7aab..74a5433 100644
--- a/nsis/gvim.nsi
+++ b/nsis/gvim.nsi
@@ -385,6 +385,7 @@
 		File ${VIMRT}\libintl-8.dll
 		File ${VIMRT}\libiconv-2.dll
 		File /nonfatal ${VIMRT}\libwinpthread-1.dll
+		File /nonfatal ${VIMRT}\libgcc_s_sjlj-1.dll
 	SectionEnd
 !endif