$MSM_PATH($msmdir) needs a path separator at the end of the line.

A error occurs in Visual Studio Express and Windows 7/8/8.1 environment,
 if a path separator at the end of the line is missing.
The registry entry for Merge Module directory has a path separator as suffix.

Change-Id: Ic1c51716631980e89f5bfa11a1d76b45c35e920e
Reviewed-on: https://gerrit.libreoffice.org/7272
Reviewed-by: Andras Timar <andras.timar@collabora.com>
Tested-by: Andras Timar <andras.timar@collabora.com>