COMP: Fix CMake 3.15 warning in SlicerLinkerAsNeededFlagCheck project

This commit fixes the following warning:

  CMake Warning (dev) in /home/jcfr/Projects/Slicer-Qt5-VTK8/CMake/SlicerLinkerAsNeededFlagCheck/CMakeLists.txt:
    No project() command is present.  The top-level CMakeLists.txt file must
    contain a literal, direct call to the project() command.  Add a line of
    code such as

      project(ProjectName)

    near the top of the file, but after cmake_minimum_required().

    CMake is pretending there is a "project(Project)" command on the first
    line.
  This warning is for project developers.  Use -Wno-dev to suppress it.

svn-url: http://viewvc.slicer.org/viewvc.cgi/Slicer4?view=revision&revision=28454
git-svn-id: http://svn.slicer.org/Slicer4/trunk@28454 3bd1e089-480b-0410-8dfb-8563597acbee

CMake/SlicerLinkerAsNeededFlagCheck/CMakeLists.txt

@@ -1,3 +1,4 @@
+project(SlicerLinkerAsNeededFlagCheck)
 add_library(A SHARED A.cxx)
 add_library(B SHARED B.cxx)
 add_executable(C C.cxx)