[clang][CFG] Assertion failure when control flow in for-loop update expression

This is a crash while building CFG.

Encountered while running clang tests with lifetime safety enabled by default:

```cpp
void pr8880_3(int first) {
for ( ; ; (void)({ if (first) { first = 0; continue; } 0; })) {}
}
```

https://godbolt.org/z/zPPsb3xPs

```
clang++: /root/llvm-project/llvm/tools/clang/lib/Analysis/CFG.cpp:3673: clang::CFGBlock* {anonymous}::CFGBuilder::VisitForStmt(clang::ForStmt*): Assertion `Block == Succ' failed.
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace, preprocessed source, and associated run script.
Stack dump:
0. Program arguments: /opt/compiler-explorer/clang-assertions-trunk/bin/clang++ -g -o /app/output.s -mllvm --x86-asm-syntax=intel -fno-verbose-asm -S --gcc-toolchain=/opt/compiler-explorer/gcc-snapshot -fcolor-diagnostics -fno-crash-diagnostics -Xclang -fexperimental-lifetime-safety -Wexperimental-lifetime-safety
1. parser at end of file
2. :1:26: parsing function body 'pr8880_3'
#0 0x00000000041f5e08 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x41f5e08)
#1 0x00000000041f3234 llvm::sys::CleanupOnSignal(unsigned long) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x41f3234)
#2 0x0000000004137498 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
#3 0x00007b05e0e42520 (/lib/x86_64-linux-gnu/libc.so.6+0x42520)
#4 0x00007b05e0e969fc pthread_kill (/lib/x86_64-linux-gnu/libc.so.6+0x969fc)
#5 0x00007b05e0e42476 gsignal (/lib/x86_64-linux-gnu/libc.so.6+0x42476)
#6 0x00007b05e0e287f3 abort (/lib/x86_64-linux-gnu/libc.so.6+0x287f3)
#7 0x00007b05e0e2871b (/lib/x86_64-linux-gnu/libc.so.6+0x2871b)
#8 0x00007b05e0e39e96 (/lib/x86_64-linux-gnu/libc.so.6+0x39e96)
#9 0x00000000076b48e4 (anonymous namespace)::CFGBuilder::VisitForStmt(clang::ForStmt*) CFG.cpp:0:0
#10 0x00000000076b7795 (anonymous namespace)::CFGBuilder::VisitCompoundStmt(clang::CompoundStmt*, bool) CFG.cpp:0:0
#11 0x00000000076b9d2c clang::CFG::buildCFG(clang::Decl const*, clang::Stmt*, clang::ASTContext*, clang::CFG::BuildOptions const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x76b9d2c)
#12 0x00000000076844d2 clang::AnalysisDeclContext::getCFG() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x76844d2)
#13 0x00000000075a2405 clang::sema::AnalysisBasedWarnings::IssueWarnings(clang::sema::AnalysisBasedWarnings::Policy, clang::sema::FunctionScopeInfo*, clang::Decl const*, clang::QualType) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x75a2405)
#14 0x0000000006a7ca9a clang::Sema::PopFunctionScopeInfo(clang::sema::AnalysisBasedWarnings::Policy const*, clang::Decl const*, clang::QualType) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6a7ca9a)
#15 0x0000000006cdd9e4 clang::Sema::ActOnFinishFunctionBody(clang::Decl*, clang::Stmt*, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6cdd9e4)
#16 0x00000000069f6dc4 clang::Parser::ParseFunctionStatementBody(clang::Decl*, clang::Parser::ParseScope&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x69f6dc4)
#17 0x00000000068fd7eb clang::Parser::ParseFunctionDefinition(clang::ParsingDeclarator&, clang::Parser::ParsedTemplateInfo const&, clang::Parser::LateParsedAttrList*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x68fd7eb)
#18 0x0000000006933c5d clang::Parser::ParseDeclGroup(clang::ParsingDeclSpec&, clang::DeclaratorContext, clang::ParsedAttributes&, clang::Parser::ParsedTemplateInfo&, clang::SourceLocation*, clang::Parser::ForRangeInit*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6933c5d)
#19 0x00000000068f0f8e clang::Parser::ParseDeclOrFunctionDefInternal(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec&, clang::AccessSpecifier) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x68f0f8e)
#20 0x00000000068f172f clang::Parser::ParseDeclarationOrFunctionDefinition(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*, clang::AccessSpecifier) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x68f172f)
#21 0x00000000068f8fe3 clang::Parser::ParseExternalDeclaration(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x68f8fe3)
#22 0x00000000068f9ef5 clang::Parser::ParseTopLevelDecl(clang::OpaquePtr&, clang::Sema::ModuleImportState&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x68f9ef5)
#23 0x00000000068fa3b0 clang::Parser::ParseFirstTopLevelDecl(clang::OpaquePtr&, clang::Sema::ModuleImportState&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x68fa3b0)
#24 0x00000000068db543 clang::ParseAST(clang::Sema&, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x68db543)
#25 0x0000000004b3e668 clang::CodeGenAction::ExecuteAction() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4b3e668)
#26 0x0000000004e2bcf5 clang::FrontendAction::Execute() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4e2bcf5)
#27 0x0000000004dacd8e clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4dacd8e)
#28 0x0000000004f2377d clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4f2377d)
#29 0x0000000000dc3800 cc1_main(llvm::ArrayRef, char const*, void*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xdc3800)
#30 0x0000000000dba36a ExecuteCC1Tool(llvm::SmallVectorImpl&, llvm::ToolContext const&, llvm::IntrusiveRefCntPtr) driver.cpp:0:0
#31 0x0000000000dba4ed int llvm::function_ref&)>::callback_fn&)>(long, llvm::SmallVectorImpl&) driver.cpp:0:0
#32 0x0000000004ba7819 void llvm::function_ref::callback_fn>, std::__cxx11::basic_string, std::allocator>*, bool*) const::'lambda'()>(long) Job.cpp:0:0
#33 0x0000000004137934 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4137934)
#34 0x0000000004ba7e2f clang::driver::CC1Command::Execute(llvm::ArrayRef>, std::__cxx11::basic_string, std::allocator>*, bool*) const (.part.0) Job.cpp:0:0
#35 0x0000000004b69142 clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4b69142)
#36 0x0000000004b6a0ee clang::driver::Compilation::ExecuteJobs(clang::driver::JobList const&, llvm::SmallVectorImpl>&, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4b6a0ee)
#37 0x0000000004b71825 clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl>&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4b71825)
#38 0x0000000000dbfd29 clang_main(int, char**, llvm::ToolContext const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xdbfd29)
#39 0x0000000000c6fab4 main (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xc6fab4)
#40 0x00007b05e0e29d90 (/lib/x86_64-linux-gnu/libc.so.6+0x29d90)
#41 0x00007b05e0e29e40 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x29e40)
#42 0x0000000000db9e05 _start (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xdb9e05)
```

Start in llvm/tools/clang/lib/Analysis/CFG.cpp, especially CFGBuilder::VisitForStmt at the assertion reported near line 3673. Reproduce the crash with the provided pr8880_3 example and the shown lifetime-safety flags, then confirm the CFG build no longer hits the assertion and cover the case with an appropriate Clang regression test.

Written by the indexing model from the issue text.