patch 8.1.1230: a lot of code is shared between vim.exe and gvim.exe

Problem:    A lot of code is shared between vim.exe and gvim.exe.
Solution:   Optionally put the shared code in vim.dll. (Ken Takata,
            closes #4287)

nsis/gvim.nsi

@@ -322,6 +322,9 @@ Section "$(str_section_exe)" id_section_exe
 
 	SetOutPath $0
 	File /oname=gvim.exe ${VIMSRC}\gvim_ole.exe
+!if /FileExists "${VIMSRC}\vim${BIT}.dll"
+	File ${VIMSRC}\vim${BIT}.dll
+!endif
 	File /oname=install.exe ${VIMSRC}\installw32.exe
 	File /oname=uninstal.exe ${VIMSRC}\uninstalw32.exe
 	File ${VIMSRC}\vimrun.exe