Fix problem with building ISPC by clang 3.4

Makefile

@@ -115,7 +115,7 @@ CXXFLAGS=$(OPT) $(LLVM_CXXFLAGS) -I. -Iobjs/ -I$(CLANG_INCLUDE)  \
 	$(LLVM_VERSION_DEF) \
 	-Wall \
 	-DBUILD_DATE="\"$(BUILD_DATE)\"" -DBUILD_VERSION="\"$(BUILD_VERSION)\"" \
-	-Wno-sign-compare
+	-Wno-sign-compare -Wno-unused-function
 ifneq ($(LLVM_VERSION),LLVM_3_1)
 	CXXFLAGS+=-Werror
 endif

cbackend.cpp

@@ -3066,7 +3066,7 @@ void CWriter::visitReturnInst(llvm::ReturnInst &I) {
   // Don't output a void return if this is the last basic block in the function
   if (I.getNumOperands() == 0 &&
       &*--I.getParent()->getParent()->end() == I.getParent() &&
-      !I.getParent()->size() == 1) {
+      (!I.getParent()->size()) == 1) {
     return;
   }