[clang] [clang][bytecode] Fix 'if consteval' in non-constant contexts (PR #104707)

[via cfe-commits]

================
@@ -4368,8 +4363,19 @@ template <class Emitter> bool Compiler<Emitter>::visitIfStmt(const IfStmt *IS) {
     if (!visitDeclStmt(CondDecl))
       return false;
 
-  if (!this->visitBool(IS->getCond()))
-    return false;
+  // Compile condition.
+  if (IS->isNonNegatedConsteval()) {
+    if (!this->emitIsConstantContext(IS))
+      return false;
+  } else if (IS->isNegatedConsteval()) {
+    if (!this->emitIsConstantContext(IS))
+      return false;
+    if (!this->emitInv(IS))
+      return false;
+  } else {
+    if (!this->visitBool(IS->getCond()))
+      return false;
+  }
----------------
cor3ntin wrote:

How would you deal with code like

```cpp
constexpr void f() {
    if !consteval {
goto a;
a:;  
}
}```

https://github.com/llvm/llvm-project/pull/104707