Minor - silence a cmake warning

[Nazalassa]

When compiling with CMake I get this warning:

Code Select Expand

CMake Warning (dev) in CMakeLists.txt:
  A logical block opening on the line

    /src/simutrans/CMakeLists.txt:380 (if)

  closes on the line

    /src/simutrans/CMakeLists.txt:399 (endif)

  with mis-matching arguments.
This warning is for project developers.  Use -Wno-dev to suppress it.

Patch: http://patches.simutrans-germany.com/download.php?file=fix-cmake-warning.patch

(Note: being new to Cmake, I do not know if it is an elegant solution.)