Enable -Wcovered-switch-default as it matches the switch style used in llvm.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@151609 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/projects/sample/Makefile.llvm.rules b/projects/sample/Makefile.llvm.rules
index f496bd4..7467d84 100644
--- a/projects/sample/Makefile.llvm.rules
+++ b/projects/sample/Makefile.llvm.rules
@@ -571,7 +571,7 @@
 CompileCommonOpts += -pedantic -Wno-long-long
 endif
 CompileCommonOpts += -Wall -W -Wno-unused-parameter -Wwrite-strings \
-                     $(EXTRA_OPTIONS)
+                     $(EXTRA_OPTIONS) $(COVERED_SWITCH_DEFAULT)
 # Enable cast-qual for C++; the workaround is to use const_cast.
 CXX.Flags += -Wcast-qual