Honour CLANG_BUILD_EXAMPLES correctly, by setting the directory's
EXCLUDE_FROM_ALL property.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@156090 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/examples/CMakeLists.txt b/examples/CMakeLists.txt
index 19d8869..84a5d2c 100644
--- a/examples/CMakeLists.txt
+++ b/examples/CMakeLists.txt
@@ -1,5 +1,5 @@
 if(NOT CLANG_BUILD_EXAMPLES)
-  set(EXCLUDE_FROM_ALL ON)
+  set_property(DIRECTORY PROPERTY EXCLUDE_FROM_ALL ON)
 endif()
 
 add_subdirectory(analyzer-plugin)