[Clang][NFC] Fix out-of-bounds access (#77193)

The changes to tablegen made by
#76825 result in
`StmtClass::lastStmtConstant` changing from `StmtClass::WhileStmtClass`
to `StmtClass::GCCAsmStmtClass`. Since `CFG::BuildOptions::alwaysAdd` is
never called with a `WhileStmt`, this has flown under the radar until
now.

Once such test in which an out-of-bounds access occurs is
`test/Sema/inline-asm-validate.c`, among many others.

clang/include/clang/Analysis/CFG.h

@@ -1215,7 +1215,9 @@ class CFG {
   //===--------------------------------------------------------------------===//
 
   class BuildOptions {
-    std::bitset<Stmt::lastStmtConstant> alwaysAddMask;
+    // Stmt::lastStmtConstant has the same value as the last Stmt kind,
+    // so make sure we add one to account for this!
+    std::bitset<Stmt::lastStmtConstant + 1> alwaysAddMask;
 
   public:
     using ForcedBlkExprs = llvm::DenseMap<const Stmt *, const CFGBlock *>;