Fix synatax of cmake expression

When CMAKE_BUILD_TYPE is not set (the default) using curly
braces will cause a syntax error.  This is copy of the same fix
from the slicer4 repository.

CMakeLists.txt

@@ -262,7 +262,7 @@ IF(CMAKE_COMPILER_IS_GNUCXX)
   # With older version of gcc supporting the flag -fstack-protector-all, an extra dependency to libssp.so
   # is introduced. If gcc is smaller than 4.4.0 and the build type is Release let's not include the flag.
   # Doing so should allow to build package made for distribution using older linux distro.
-  IF(${GCC_VERSION} VERSION_GREATER "4.4.0" OR (DEFINED CMAKE_BUILD_TYPE AND ${CMAKE_BUILD_TYPE} STREQUAL "Debug" AND ${GCC_VERSION} VERSION_LESS "4.4.0"))
+  IF(${GCC_VERSION} VERSION_GREATER "4.4.0" OR (CMAKE_BUILD_TYPE STREQUAL "Debug" AND ${GCC_VERSION} VERSION_LESS "4.4.0"))
     ctkFunctionCheckCompilerFlags("-fstack-protector-all" cflags)
   ENDIF()
   IF(MINGW)