[analyzer] ConstraintManager - use EXPENSIVE_CHECKS instead of (gcc specific) __OPTIMIZE__ guard

This was noticed on D71817, which removed another use of __OPTIMIZE__

Differential Revision: https://reviews.llvm.org/D76622

clang/include/clang/StaticAnalyzer/Core/PathSensitive/ConstraintManager.h

@@ -96,11 +96,7 @@ public:
     // If StTrue is infeasible, asserting the falseness of Cond is unnecessary
     // because the existing constraints already establish this.
     if (!StTrue) {
-#ifndef __OPTIMIZE__
-      // This check is expensive and should be disabled even in Release+Asserts
-      // builds.
-      // FIXME: __OPTIMIZE__ is a GNU extension that Clang implements but MSVC
-      // does not. Is there a good equivalent there?
+#ifdef EXPENSIVE_CHECKS
       assert(assume(State, Cond, false) && "System is over constrained.");
 #endif
       return ProgramStatePair((ProgramStateRef)nullptr, State);