Don't build examples by default, use BUILD_EXAMPLES=1 to build them. The only utility of this is testing that we keep the examples up to date, I will just make the buildbots run with this flag.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@88979 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/Makefile b/Makefile
index 671f92c..31c1b69 100644
--- a/Makefile
+++ b/Makefile
@@ -32,7 +32,11 @@
 else
   DIRS := lib/System lib/Support utils lib/VMCore lib tools/llvm-config \
           tools runtime docs unittests
-  OPTIONAL_DIRS := examples projects bindings
+  OPTIONAL_DIRS := projects bindings
+endif
+
+ifeq ($(BUILD_EXAMPLES),1)
+  OPTIONAL_DIRS += examples
 endif
 
 EXTRA_DIST := test unittests llvm.spec include win32 Xcode