CMakeLists: Apply compilation flags to the sirit target

Previously this wasn't utilizing any of the compiler flags, meaning it
wasn't applying any of the specified warnings.

Since applying the warnings to the target, this uncovered a few warning
cases, such as shadowing class variables on MSVC, etc, which have been fixed.

src/op.cpp

@@ -67,8 +67,8 @@ void Op::Sink(Operand* operand) {
     operand_store.push_back(std::unique_ptr<Operand>(operand));
 }
 
-void Op::Sink(const std::vector<Operand*>& operands) {
-    for (auto* operand : operands) {
+void Op::Sink(const std::vector<Operand*>& operands_) {
+    for (auto* operand : operands_) {
         Sink(operand);
     }
 }