[clang] Assertion `Result && "Could not evaluate expression"' failed with __builtin_object_size in enable_if

Reproducer:
https://godbolt.org/z/ET4GMGbrb

With an assertion-enabled Clang trunk build in C++ mode:

```c
int fun(int x) { int y = x; return y; }

int strnlen(char *s, int maxlen)
__attribute__( (
enable_if( __builtin_object_size(s, fun(0) ) ,"!") ) )
{
return 0;
}
```

Backtrace:

```
clang++: /root/llvm-project/llvm/tools/clang/lib/AST/ExprConstant.cpp:22192: 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 and dumped files.
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. :6:1: current parser token '{'
#0 0x0000000004468688 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4468688)
#1 0x0000000004465534 llvm::sys::RunSignalHandlers() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4465534)
#2 0x0000000004465b6c llvm::sys::CleanupOnSignal(unsigned long) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4465b6c)
#3 0x00000000043a4448 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
#4 0x0000788cb4445330 (/lib/x86_64-linux-gnu/libc.so.6+0x45330)
#5 0x0000788cb449ec0c pthread_kill (/lib/x86_64-linux-gnu/libc.so.6+0x9ec0c)
#6 0x0000788cb444527e raise (/lib/x86_64-linux-gnu/libc.so.6+0x4527e)
#7 0x0000788cb44288ff abort (/lib/x86_64-linux-gnu/libc.so.6+0x288ff)
#8 0x0000788cb442881b (/lib/x86_64-linux-gnu/libc.so.6+0x2881b)
#9 0x0000788cb443b517 (/lib/x86_64-linux-gnu/libc.so.6+0x3b517)
#10 0x00000000081727e9 clang::Expr::EvaluateKnownConstInt(clang::ASTContext const&) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x81727e9)
#11 0x00000000081d074a (anonymous namespace)::IntExprEvaluator::VisitBuiltinCallExpr(clang::CallExpr const*, unsigned int) ExprConstant.cpp:0:0
#12 0x00000000081d670b (anonymous namespace)::IntExprEvaluator::VisitCallExpr(clang::CallExpr const*) ExprConstant.cpp:0:0
#13 0x00000000081973d8 clang::StmtVisitorBase::Visit(clang::Stmt const*) ExprConstant.cpp:0:0
#14 0x000000000816a0ff Evaluate(clang::APValue&, (anonymous namespace)::EvalInfo&, clang::Expr const*) ExprConstant.cpp:0:0
#15 0x0000000008174548 EvaluateAsBooleanCondition(clang::Expr const*, bool&, (anonymous namespace)::EvalInfo&) ExprConstant.cpp:0:0
#16 0x00000000081c910b (anonymous namespace)::IntExprEvaluator::VisitCastExpr(clang::CastExpr const*) ExprConstant.cpp:0:0
#17 0x00000000081984bc clang::StmtVisitorBase::Visit(clang::Stmt const*) ExprConstant.cpp:0:0
#18 0x000000000816a0ff Evaluate(clang::APValue&, (anonymous namespace)::EvalInfo&, clang::Expr const*) ExprConstant.cpp:0:0
#19 0x000000000817c0ee clang::Expr::isPotentialConstantExprUnevaluated(clang::Expr*, clang::FunctionDecl const*, llvm::SmallVectorImpl>&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x817c0ee)
#20 0x00000000071d1cd0 checkFunctionConditionAttr(clang::Sema&, clang::Decl*, clang::ParsedAttr const&, clang::Expr*&, llvm::StringRef&) (.part.0) SemaDeclAttr.cpp:0:0
#21 0x00000000071eb5c3 handleEnableIfAttr(clang::Sema&, clang::Decl*, clang::ParsedAttr const&) SemaDeclAttr.cpp:0:0
#22 0x0000000007209c20 ProcessDeclAttribute(clang::Sema&, clang::Scope*, clang::Decl*, clang::ParsedAttr const&, clang::Sema::ProcessDeclAttributeOptions const&) (.isra.0) SemaDeclAttr.cpp:0:0
#23 0x000000000720c1db clang::Sema::ProcessDeclAttributes(clang::Scope*, clang::Decl*, clang::Declarator const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x720c1db)
#24 0x00000000071b9a4b clang::Sema::ActOnFunctionDeclarator(clang::Scope*, clang::Declarator&, clang::DeclContext*, clang::TypeSourceInfo*, clang::LookupResult&, llvm::MutableArrayRef, bool&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x71b9a4b)
#25 0x00000000071c05ab clang::Sema::HandleDeclarator(clang::Scope*, clang::Declarator&, llvm::MutableArrayRef) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x71c05ab)
#26 0x00000000071c1238 clang::Sema::ActOnStartOfFunctionDef(clang::Scope*, clang::Declarator&, llvm::MutableArrayRef, clang::SkipBodyInfo*, clang::Sema::FnBodyKind) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x71c1238)
#27 0x0000000006d99a0f clang::Parser::ParseFunctionDefinition(clang::ParsingDeclarator&, clang::Parser::ParsedTemplateInfo const&, clang::LateParsedAttrList*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6d99a0f)
#28 0x0000000006de3c86 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+++0x6de3c86)
#29 0x0000000006d8e64b clang::Parser::ParseDeclOrFunctionDefInternal(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec&, clang::AccessSpecifier) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6d8e64b)
#30 0x0000000006d8ee3f clang::Parser::ParseDeclarationOrFunctionDefinition(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*, clang::AccessSpecifier) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6d8ee3f)
#31 0x0000000006d9b5f8 clang::Parser::ParseExternalDeclaration(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6d9b5f8)
#32 0x0000000006d9c555 clang::Parser::ParseTopLevelDecl(clang::OpaquePtr&, clang::Sema::ModuleImportState&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6d9c555)
#33 0x0000000006d794aa clang::ParseAST(clang::Sema&, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6d794aa)
#34 0x0000000004f62718 clang::CodeGenAction::ExecuteAction() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4f62718)
#35 0x000000000528edf8 clang::FrontendAction::Execute() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x528edf8)
#36 0x000000000521bf8d clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x521bf8d)
#37 0x0000000005364abd clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5364abd)
#38 0x0000000000dabaac cc1_main(llvm::ArrayRef, char const*, void*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xdabaac)
#39 0x0000000000da26ca ExecuteCC1Tool(llvm::SmallVectorImpl&, llvm::ToolContext const&, llvm::IntrusiveRefCntPtr) driver.cpp:0:0
#40 0x0000000000da284d int llvm::function_ref&)>::callback_fn&)>(long, llvm::SmallVectorImpl&) driver.cpp:0:0
#41 0x0000000004fdb1f9 void llvm::function_ref::callback_fn>, std::__cxx11::basic_string, std::allocator>*, bool*) const::'lambda'()>(long) Job.cpp:0:0
#42 0x00000000043a4884 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x43a4884)
#43 0x0000000004fdbd65 clang::driver::CC1Command::Execute(llvm::ArrayRef>, std::__cxx11::basic_string, std::allocator>*, bool*) const (.part.0) Job.cpp:0:0
#44 0x0000000004f93c12 clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4f93c12)
#45 0x0000000004f98577 clang::driver::Compilation::ExecuteJobs(clang::driver::JobList const&, llvm::SmallVectorImpl>&, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4f98577)
#46 0x0000000004fa2ae5 clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl>&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4fa2ae5)
#47 0x0000000000da7faa clang_main(int, char**, llvm::ToolContext const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xda7faa)
#48 0x0000000000cc3c5a main (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xcc3c5a)
#49 0x0000788cb442a1ca (/lib/x86_64-linux-gnu/libc.so.6+0x2a1ca)
#50 0x0000788cb442a28b __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x2a28b)
#51 0x0000000000da2075 _start (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xda2075)
clang++: error: clang frontend command failed due to signal (use -v to see invocation)
Compiler returned: 134
```

This reproduces all the way back to Clang 9.0.0
This testcase was generated by fuzzer.

Start by reproducing the compiler assertion with the Godbolt testcase in C++ mode using an assertion-enabled Clang build. Read llvm-project/clang/lib/AST/ExprConstant.cpp and the enable_if handling in SemaDeclAttr.cpp, following the stack from EvaluateKnownConstInt; done means the testcase no longer aborts with the reported assertion and the behavior is covered by a regression test.

Written by the indexing model from the issue text.