Fix a -Wcovered-switch-default warning in emitJumpTables.

Makefile.standalone

 # The following variables will likely need to be modified, depending on where
 # and how you built LLVM & Clang. They can be overridden in a command-line
 # invocation of make, like:
 #
 #   make LLVM_SRC_PATH=<path> LIBCXX_INSTALL_PATH=<path> CLANG_PATH=<path> \
 #        PNACL_BIN_PATH=<path> ...
 #
 
 # LLVM_SRC_PATH is the path to the root of the checked out source code. This
 # directory should contain the configure script, the include/ and lib/
@@ skipping 141 matching lines @@
                 `$(PNACL_BIN_PATH)/llvm-config --ldflags` \
                 `$(PNACL_BIN_PATH)/llvm-config --system-libs`
 SB_LLVM_LDFLAGS := $(LLVM_LIBS_LIST) \
                    -L$(SB_LLVM_PATH)/lib
 
 CCACHE := `command -v ccache`
 CXX := CCACHE_CPP2=yes $(CCACHE) $(CLANG_PATH)/clang++
 SB_CXX := CCACHE_CPP2=yes $(CCACHE) $(PNACL_BIN_PATH)/pnacl-clang++
 SB_TRANSLATE := $(PNACL_BIN_PATH)/pnacl-translate
 
+# Extra warnings that LLVM's build system adds in addition to -Wall.
+LLVM_EXTRA_WARNINGS := -Wcovered-switch-default
+
 BASE_CXXFLAGS := -std=gnu++11 -Wall -Wextra -Werror -fno-rtti \
         -fno-exceptions $(OPTLEVEL) $(ASSERTIONS) -g -pedantic \
-        $(CXX_EXTRA)
+        $(LLVM_EXTRA_WARNINGS) $(CXX_EXTRA)
 
 CXXFLAGS := $(LLVM_CXXFLAGS) $(BASE_CXXFLAGS) $(CXX_DEFINES) $(HOST_FLAGS) \
         $(STDLIB_FLAGS)
 SB_CXXFLAGS := $(SB_LLVM_CXXFLAGS) $(BASE_CXXFLAGS) $(SB_CXX_DEFINES)
 
 LDFLAGS := $(HOST_FLAGS) -L$(LIBCXX_INSTALL_PATH)/lib -Wl,--gc-sections \
         $(LD_EXTRA) $(STDLIB_FLAGS)
 # Not specifying -Wl,--gc-sections but instead doing bitcode linking GC w/ LTO.
 SB_LDFLAGS := $(LINKOPTLEVEL) $(LD_EXTRA)
 
@@ skipping 203 matching lines @@
 
 docs:
         doxygen Doxyfile
         @echo See file://`pwd`/docs/html/index.html
 
 clean:
         rm -rf pnacl-sz *.o $(OBJDIR) $(SB_OBJDIR) build/pnacl-sz.bloat.json
 
 clean-all: clean
         rm -rf build/ docs/