CMakeLists.txt: FORCE the default of CMAKE_BUILD_TYPE to Release

The existing logic to default the CMAKE_BUILT_TYPE to Release did not
actually work without the FORCE parameter on the set().

git-svn-id: https://llvm.org/svn/llvm-project/test-suite/trunk@292686 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/CMakeLists.txt b/CMakeLists.txt
index d1ff7cd..9037007 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -8,7 +8,7 @@
 # falls over unless -DNDEBUG is set.
 if(NOT CMAKE_BUILD_TYPE AND NOT CMAKE_CONFIGURATION_TYPES)
   message(STATUS "No build type selected, defaulting to Release")
-  set(CMAKE_BUILD_TYPE "Release" CACHE STRING "")
+  set(CMAKE_BUILD_TYPE "Release" CACHE STRING "" FORCE)
 endif()
 # Selecting installation directories or build types is untypical.
 mark_as_advanced(CMAKE_INSTALL_PREFIX CMAKE_BUILD_TYPE)