[clang] assertion failure clang::Sema::mergeErrorAttr SemaDeclAttr.cpp

The following code:

```cpp
[[gnu::warning("do not call")]]
[[gnu::warning("do not call")]]
static inline void level1(void) {}
```

Resulted in this output:
```
clang++: /home/fuzz/WorkSpace/fusion-fuzz/projects/clang/llvm-project/clang/lib/Sema/SemaDeclAttr.cpp:4059: clang::ErrorAttr* clang::Sema::mergeErrorAttr(clang::Decl*, const clang::AttributeCommonInfo&, llvm::StringRef): Assertion `(NewAttr == "error" || NewAttr == "warning") && "unexpected normalized full name"' 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: /home/fuzz/WorkSpace/fusion-fuzz/projects/clang/llvm-clang-install/bin/clang++ -S -o /dev/null -O3 -std=c++20 /tmp/test.cpp
1. /tmp/test.cpp:3:33: current parser token '{'
#0 0x0000559ee45d23e7 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/home/fuzz/WorkSpace/fusion-fuzz/projects/clang/llvm-clang-install/bin/clang+++0x24923e7)
#1 0x0000559ee45cfdc4 llvm::sys::CleanupOnSignal(unsigned long) (/home/fuzz/WorkSpace/fusion-fuzz/projects/clang/llvm-clang-install/bin/clang+++0x248fdc4)
#2 0x0000559ee450e218 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
#3 0x00007fa320d62970 (/usr/lib/x86_64-linux-gnu/libc.so.6+0x40970)
#4 0x00007fa320db91dc (/usr/lib/x86_64-linux-gnu/libc.so.6+0x971dc)
#5 0x00007fa320d62842 raise (/usr/lib/x86_64-linux-gnu/libc.so.6+0x40842)
#6 0x00007fa320d4a4b2 abort (/usr/lib/x86_64-linux-gnu/libc.so.6+0x284b2)
#7 0x00007fa320d4a424 __assert_perror_fail (/usr/lib/x86_64-linux-gnu/libc.so.6+0x28424)
#8 0x0000559ee2d59b25 clang::Sema::mergeErrorAttr(clang::Decl*, clang::AttributeCommonInfo const&, llvm::StringRef) (.cold) SemaDeclAttr.cpp:0:0
#9 0x0000559ee706e797 ProcessDeclAttribute(clang::Sema&, clang::Scope*, clang::Decl*, clang::ParsedAttr const&, clang::Sema::ProcessDeclAttributeOptions const&) SemaDeclAttr.cpp:0:0
#10 0x0000559ee707005a clang::Sema::ProcessDeclAttributes(clang::Scope*, clang::Decl*, clang::Declarator const&) (/home/fuzz/WorkSpace/fusion-fuzz/projects/clang/llvm-clang-install/bin/clang+++0x4f3005a)
#11 0x0000559ee702253d clang::Sema::ActOnFunctionDeclarator(clang::Scope*, clang::Declarator&, clang::DeclContext*, clang::TypeSourceInfo*, clang::LookupResult&, llvm::MutableArrayRef, bool&) (/home/fuzz/WorkSpace/fusion-fuzz/projects/clang/llvm-clang-install/bin/clang+++0x4ee253d)
#12 0x0000559ee7027752 clang::Sema::HandleDeclarator(clang::Scope*, clang::Declarator&, llvm::MutableArrayRef) (/home/fuzz/WorkSpace/fusion-fuzz/projects/clang/llvm-clang-install/bin/clang+++0x4ee7752)
#13 0x0000559ee702819f clang::Sema::ActOnStartOfFunctionDef(clang::Scope*, clang::Declarator&, llvm::MutableArrayRef, clang::SkipBodyInfo*, clang::Sema::FnBodyKind) (/home/fuzz/WorkSpace/fusion-fuzz/projects/clang/llvm-clang-install/bin/clang+++0x4ee819f)
#14 0x0000559ee6c400e3 clang::Parser::ParseFunctionDefinition(clang::ParsingDeclarator&, clang::Parser::ParsedTemplateInfo const&, clang::LateParsedAttrList*) (/home/fuzz/WorkSpace/fusion-fuzz/projects/clang/llvm-clang-install/bin/clang+++0x4b000e3)
#15 0x0000559ee6c91671 clang::Parser::ParseDeclGroup(clang::ParsingDeclSpec&, clang::DeclaratorContext, clang::ParsedAttributes&, clang::Parser::ParsedTemplateInfo&, clang::SourceLocation*, clang::Parser::ForRangeInit*) (/home/fuzz/WorkSpace/fusion-fuzz/projects/clang/llvm-clang-install/bin/clang+++0x4b51671)
#16 0x0000559ee6c399af clang::Parser::ParseDeclOrFunctionDefInternal(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec&, clang::AccessSpecifier) (/home/fuzz/WorkSpace/fusion-fuzz/projects/clang/llvm-clang-install/bin/clang+++0x4af99af)
#17 0x0000559ee6c3a10f clang::Parser::ParseDeclarationOrFunctionDefinition(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*, clang::AccessSpecifier) (/home/fuzz/WorkSpace/fusion-fuzz/projects/clang/llvm-clang-install/bin/clang+++0x4afa10f)
#18 0x0000559ee6c453ea clang::Parser::ParseExternalDeclaration(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*) (/home/fuzz/WorkSpace/fusion-fuzz/projects/clang/llvm-clang-install/bin/clang+++0x4b053ea)
#19 0x0000559ee6c4638d clang::Parser::ParseTopLevelDecl(clang::OpaquePtr&, clang::Sema::ModuleImportState&) (/home/fuzz/WorkSpace/fusion-fuzz/projects/clang/llvm-clang-install/bin/clang+++0x4b0638d)
#20 0x0000559ee6c46791 clang::Parser::ParseFirstTopLevelDecl(clang::OpaquePtr&, clang::Sema::ModuleImportState&) (/home/fuzz/WorkSpace/fusion-fuzz/projects/clang/llvm-clang-install/bin/clang+++0x4b06791)
#21 0x0000559ee6c2550c clang::ParseAST(clang::Sema&, bool, bool) (/home/fuzz/WorkSpace/fusion-fuzz/projects/clang/llvm-clang-install/bin/clang+++0x4ae550c)
#22 0x0000559ee521c65a clang::FrontendAction::Execute() (/home/fuzz/WorkSpace/fusion-fuzz/projects/clang/llvm-clang-install/bin/clang+++0x30dc65a)
#23 0x0000559ee51a370a clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/home/fuzz/WorkSpace/fusion-fuzz/projects/clang/llvm-clang-install/bin/clang+++0x306370a)
#24 0x0000559ee52ea71a clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/home/fuzz/WorkSpace/fusion-fuzz/projects/clang/llvm-clang-install/bin/clang+++0x31aa71a)
#25 0x0000559ee30a88f3 cc1_main(llvm::ArrayRef, char const*, void*) (/home/fuzz/WorkSpace/fusion-fuzz/projects/clang/llvm-clang-install/bin/clang+++0xf688f3)
#26 0x0000559ee30a02b8 ExecuteCC1Tool(llvm::SmallVectorImpl&, llvm::ToolContext const&, llvm::IntrusiveRefCntPtr) driver.cpp:0:0
#27 0x0000559ee30a048a int llvm::function_ref&)>::callback_fn&)>(long, llvm::SmallVectorImpl&) driver.cpp:0:0
#28 0x0000559ee4f16529 void llvm::function_ref::callback_fn>, std::__cxx11::basic_string, std::allocator>*, bool*) const::'lambda'()>(long) Job.cpp:0:0
#29 0x0000559ee450e5d1 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref) (/home/fuzz/WorkSpace/fusion-fuzz/projects/clang/llvm-clang-install/bin/clang+++0x23ce5d1)
#30 0x0000559ee4f1799b clang::driver::CC1Command::Execute(llvm::ArrayRef>, std::__cxx11::basic_string, std::allocator>*, bool*) const (.part.0) Job.cpp:0:0
#31 0x0000559ee4ecaef8 clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const (/home/fuzz/WorkSpace/fusion-fuzz/projects/clang/llvm-clang-install/bin/clang+++0x2d8aef8)
#32 0x0000559ee4ed018d clang::driver::Compilation::ExecuteJobs(clang::driver::JobList const&, llvm::SmallVectorImpl>&, bool) const (/home/fuzz/WorkSpace/fusion-fuzz/projects/clang/llvm-clang-install/bin/clang+++0x2d9018d)
#33 0x0000559ee4ee30e5 clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl>&) (/home/fuzz/WorkSpace/fusion-fuzz/projects/clang/llvm-clang-install/bin/clang+++0x2da30e5)
#34 0x0000559ee30a5534 clang_main(int, char**, llvm::ToolContext const&) (/home/fuzz/WorkSpace/fusion-fuzz/projects/clang/llvm-clang-install/bin/clang+++0xf65534)
#35 0x0000559ee2feabc5 main (/home/fuzz/WorkSpace/fusion-fuzz/projects/clang/llvm-clang-install/bin/clang+++0xeaabc5)
#36 0x00007fa320d4bf77 (/usr/lib/x86_64-linux-gnu/libc.so.6+0x29f77)
#37 0x00007fa320d4c027 __libc_start_main (/usr/lib/x86_64-linux-gnu/libc.so.6+0x2a027)
#38 0x0000559ee309f521 _start (/home/fuzz/WorkSpace/fusion-fuzz/projects/clang/llvm-clang-install/bin/clang+++0xf5f521)
clang++: error: clang frontend command failed due to signal (use -v to see invocation)
clang version 24.0.0git (https://github.com/llvm/llvm-project.git 353729bbe4c53086c9acf3a9d1a4a88a61eec997)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /home/fuzz/WorkSpace/fusion-fuzz/projects/clang/llvm-clang-install/bin
Build config: +assertions
clang++: note: diagnostic msg:
********************

PLEASE ATTACH THE FOLLOWING CRASH REPRODUCER FILES TO THE BUG REPORT:
clang++: note: diagnostic msg: /tmp/test-5d1304.cpp
clang++: note: diagnostic msg: /tmp/test-5d1304.sh
clang++: note: diagnostic msg:

********************
Aborted (core dumped)
```

To reproduce:
```
/home/fuzz/WorkSpace/fusion-fuzz/projects/clang/llvm-clang-install/bin/clang++ ./test.cpp
```

Compiler version:
```
clang version 24.0.0git (https://github.com/llvm/llvm-project.git 353729bbe4c53086c9acf3a9d1a4a88a61eec997)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /home/fuzz/WorkSpace/fusion-fuzz/projects/clang/llvm-clang-install/bin
Build config: +assertions
```

*This bug was found by [fusion-fuzz](https://github.com/fusion-fuzz/fusion-fuzz)*

Start with clang/lib/Sema/SemaDeclAttr.cpp at Sema::mergeErrorAttr, using the duplicate [[gnu::warning]] declarations in test.cpp as the reproducer. Run the clang++ command from the issue, then trace how the attributes are normalized and merged. Done means the reproducer no longer triggers an assertion, with regression coverage for this case.

Written by the indexing model from the issue text.