Address CMP0054 warning for CMP0054
Address CMP0054 warning for CMP0054

This patch addresses the following warning:

CMake Warning (dev) at CMakeLists.txt:13 (if):
  Policy CMP0054 is not set: Only interpret if() arguments as
  variables or
  keywords when unquoted.  Run "cmake --help-policy CMP0054" for
  policy
  details.  Use the cmake_policy command to set the policy and
  suppress this
  warning.

  Quoted variables like "MSVC" will no longer be dereferenced when the
  policy
  is set to NEW.  Since the policy is not set the OLD behavior will be
  used.
This warning is for project developers.  Use -Wno-dev to suppress it.

Change-Id: I5402d956d6847adffe74af32370d9e568c862ac9

richardbeare/SimpleITK,InsightSoftwareConsortium/SimpleITK,kaspermarstal/SimpleElastix,richardbeare/SimpleITK,blowekamp/SimpleITK,blowekamp/SimpleITK,InsightSoftwareConsortium/SimpleITK,SimpleITK/SimpleITK,blowekamp/SimpleITK,richardbeare/SimpleITK,kaspermarstal/SimpleElastix,InsightSoftwareConsortium/SimpleITK,SimpleITK/SimpleITK,blowekamp/SimpleITK,InsightSoftwareConsortium/SimpleITK,blowekamp/SimpleITK,SimpleITK/SimpleITK,SimpleITK/SimpleITK,richardbeare/SimpleITK,blowekamp/SimpleITK,SimpleITK/SimpleITK,kaspermarstal/SimpleElastix,kaspermarstal/SimpleElastix,InsightSoftwareConsortium/SimpleITK,InsightSoftwareConsortium/SimpleITK,kaspermarstal/SimpleElastix,SimpleITK/SimpleITK,richardbeare/SimpleITK,richardbeare/SimpleITK,InsightSoftwareConsortium/SimpleITK,InsightSoftwareConsortium/SimpleITK,kaspermarstal/SimpleElastix,SimpleITK/SimpleITK,richardbeare/SimpleITK,kaspermarstal/SimpleElastix,blowekamp/SimpleITK,SimpleITK/SimpleITK,richardbeare/SimpleITK,blowekamp/SimpleITK