[clang-fuzzer] Crash in llvm::APSInt

Hi, while testing clang by AFL++, it found a crashing case:
version : llvmorg-21.1.8

PoC:

```c
void fn_40_b(const char *(*a4(int *__cdecl f2()))[(__builtin_expect(
-((sizeof(bool[1 / (((sizeof(__builtin_printf("Setup")) % 2)))]))), 0))]

) {}
```

Reduced and modified from the original:
https://godbolt.org/z/qMMG71Pj8

backtrace:

```
clang++: /root/llvm-project/llvm/tools/clang/lib/AST/ExprConstant.cpp:20808: llvm::APSInt clang::Expr::EvaluateKnownConstInt(const clang::ASTContext&) const: Assertion `Result && "Could not evaluate expression"' 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
1. parser at end of file
2. :1:6: LLVM IR generation of declaration 'fn_40_b'
3. :1:6: Generating code for declaration 'fn_40_b'
4. :1:6: Mangling declaration 'fn_40_b'
#0 0x00000000042ef648 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x42ef648)
#1 0x00000000042eca74 llvm::sys::CleanupOnSignal(unsigned long) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x42eca74)
#2 0x0000000004231818 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
#3 0x0000703a8f842520 (/lib/x86_64-linux-gnu/libc.so.6+0x42520)
#4 0x0000703a8f8969fc pthread_kill (/lib/x86_64-linux-gnu/libc.so.6+0x969fc)
#5 0x0000703a8f842476 gsignal (/lib/x86_64-linux-gnu/libc.so.6+0x42476)
#6 0x0000703a8f8287f3 abort (/lib/x86_64-linux-gnu/libc.so.6+0x287f3)
#7 0x0000703a8f82871b (/lib/x86_64-linux-gnu/libc.so.6+0x2871b)
#8 0x0000703a8f839e96 (/lib/x86_64-linux-gnu/libc.so.6+0x39e96)
#9 0x0000000007d164a9 clang::Expr::EvaluateKnownConstInt(clang::ASTContext const&) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x7d164a9)
#10 0x0000000007fe745e (anonymous namespace)::CXXNameMangler::mangleExpression(clang::Expr const*, unsigned int, bool) ItaniumMangle.cpp:0:0
#11 0x0000000007fe6b32 (anonymous namespace)::CXXNameMangler::mangleExpression(clang::Expr const*, unsigned int, bool) ItaniumMangle.cpp:0:0
#12 0x0000000007fe82fc (anonymous namespace)::CXXNameMangler::mangleExpression(clang::Expr const*, unsigned int, bool) ItaniumMangle.cpp:0:0
#13 0x0000000007fdd83b (anonymous namespace)::CXXNameMangler::mangleType(clang::QualType) ItaniumMangle.cpp:0:0
#14 0x0000000007fdd865 (anonymous namespace)::CXXNameMangler::mangleType(clang::QualType) ItaniumMangle.cpp:0:0
#15 0x0000000007feb036 (anonymous namespace)::CXXNameMangler::mangleBareFunctionType(clang::FunctionProtoType const*, bool, clang::FunctionDecl const*) ItaniumMangle.cpp:0:0
#16 0x0000000007febb35 (anonymous namespace)::CXXNameMangler::mangleType(clang::FunctionProtoType const*) ItaniumMangle.cpp:0:0
#17 0x0000000007fde0d0 (anonymous namespace)::CXXNameMangler::mangleType(clang::QualType) ItaniumMangle.cpp:0:0
#18 0x0000000007fdd865 (anonymous namespace)::CXXNameMangler::mangleType(clang::QualType) ItaniumMangle.cpp:0:0
#19 0x0000000007feb0de (anonymous namespace)::CXXNameMangler::mangleBareFunctionType(clang::FunctionProtoType const*, bool, clang::FunctionDecl const*) ItaniumMangle.cpp:0:0
#20 0x0000000007fec705 (anonymous namespace)::CXXNameMangler::mangleFunctionEncoding(clang::GlobalDecl) ItaniumMangle.cpp:0:0
#21 0x0000000007fed817 (anonymous namespace)::CXXNameMangler::mangle(clang::GlobalDecl) ItaniumMangle.cpp:0:0
#22 0x0000000007fefeb1 (anonymous namespace)::ItaniumMangleContextImpl::mangleCXXName(clang::GlobalDecl, llvm::raw_ostream&) ItaniumMangle.cpp:0:0
#23 0x000000000801573c clang::MangleContext::mangleName(clang::GlobalDecl, llvm::raw_ostream&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x801573c)
#24 0x00000000048949e5 getMangledNameImpl(clang::CodeGen::CodeGenModule&, clang::GlobalDecl, clang::NamedDecl const*, bool) CodeGenModule.cpp:0:0
#25 0x00000000048ac02d clang::CodeGen::CodeGenModule::getMangledName(clang::GlobalDecl) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x48ac02d)
#26 0x00000000048e8ce5 clang::CodeGen::CodeGenModule::GetAddrOfFunction(clang::GlobalDecl, llvm::Type*, bool, bool, clang::CodeGen::ForDefinition_t) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x48e8ce5)
#27 0x00000000048e9261 clang::CodeGen::CodeGenModule::EmitGlobalFunctionDefinition(clang::GlobalDecl, llvm::GlobalValue*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x48e9261)
#28 0x00000000048e3fe4 clang::CodeGen::CodeGenModule::EmitGlobalDefinition(clang::GlobalDecl, llvm::GlobalValue*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x48e3fe4)
#29 0x00000000048e47c3 clang::CodeGen::CodeGenModule::EmitGlobal(clang::GlobalDecl) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x48e47c3)
#30 0x00000000048efd53 clang::CodeGen::CodeGenModule::EmitTopLevelDecl(clang::Decl*) (.part.0) CodeGenModule.cpp:0:0
#31 0x0000000004c53569 (anonymous namespace)::CodeGeneratorImpl::HandleTopLevelDecl(clang::DeclGroupRef) ModuleBuilder.cpp:0:0
#32 0x0000000004c44094 clang::BackendConsumer::HandleTopLevelDecl(clang::DeclGroupRef) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4c44094)
#33 0x0000000006a0c304 clang::ParseAST(clang::Sema&, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6a0c304)
#34 0x0000000004c50978 clang::CodeGenAction::ExecuteAction() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4c50978)
#35 0x0000000004f46ff5 clang::FrontendAction::Execute() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4f46ff5)
#36 0x0000000004ec728e clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4ec728e)
#37 0x000000000504137d clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x504137d)
#38 0x0000000000de5c4c cc1_main(llvm::ArrayRef, char const*, void*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xde5c4c)
#39 0x0000000000ddc69a ExecuteCC1Tool(llvm::SmallVectorImpl&, llvm::ToolContext const&, llvm::IntrusiveRefCntPtr) driver.cpp:0:0
#40 0x0000000000ddc81d int llvm::function_ref&)>::callback_fn&)>(long, llvm::SmallVectorImpl&) driver.cpp:0:0
#41 0x0000000004cc3049 void llvm::function_ref::callback_fn>, std::__cxx11::basic_string, std::allocator>*, bool*) const::'lambda'()>(long) Job.cpp:0:0
#42 0x0000000004231cb4 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4231cb4)
#43 0x0000000004cc365f clang::driver::CC1Command::Execute(llvm::ArrayRef>, std::__cxx11::basic_string, std::allocator>*, bool*) const (.part.0) Job.cpp:0:0
#44 0x0000000004c84142 clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4c84142)
#45 0x0000000004c850ee clang::driver::Compilation::ExecuteJobs(clang::driver::JobList const&, llvm::SmallVectorImpl>&, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4c850ee)
#46 0x0000000004c8c545 clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl>&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4c8c545)
#47 0x0000000000de2041 clang_main(int, char**, llvm::ToolContext const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xde2041)
#48 0x0000000000c8d094 main (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xc8d094)
#49 0x0000703a8f829d90 (/lib/x86_64-linux-gnu/libc.so.6+0x29d90)
#50 0x0000703a8f829e40 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x29e40)
#51 0x0000000000ddc135 _start (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xddc135)
clang++: error: clang frontend command failed with exit code 134 (use -v to see invocation)
Compiler returned: 134
```

Start by reproducing the crash with the provided PoC using an assertion-enabled clang++ build. Read clang/lib/AST/ExprConstant.cpp around EvaluateKnownConstInt and follow the mangleExpression path in ItaniumMangle.cpp shown in the backtrace. Done means the reproducer no longer aborts and a regression test covers it.

Written by the indexing model from the issue text.