[clang] assertion failure at clang::Sema::CheckVectorConditionalTypes

https://godbolt.org/z/6asnrYYY6

The following code:

```cpp
static long ffl_fusion = (long)(g);
using FourFloats = float __attribute__((ext_vector_type(4)));
FourShorts four_shorts;
using FourShortsVS = short __attribute__((__vector_size__(8)));
void mix_vector_types() {
FourShortsVS vs;
(four_shorts == 1 ? vs : ffl_fusion);
}
```

Resulted in this output:
```
/tmp/test.cpp:1:33: error: use of undeclared identifier 'g'
1 | static long ffl_fusion = (long)(g);
| ^
/tmp/test.cpp:3:1: error: unknown type name 'FourShorts'; did you mean 'FourFloats'?
3 | FourShorts four_shorts;
| ^~~~~~~~~~
| FourFloats
/tmp/test.cpp:2:7: note: 'FourFloats' declared here
2 | using FourFloats = float __attribute__((ext_vector_type(4)));
| ^
clang++: /home/fuzz/WorkSpace/fusion-fuzz/projects/clang/llvm-project/clang/lib/Sema/SemaExprCXX.cpp:5890: clang::QualType clang::Sema::CheckVectorConditionalTypes(clang::ExprResult&, clang::ExprResult&, clang::ExprResult&, clang::SourceLocation): Assertion `!ResultType.isNull() && (ResultType->isVectorType() || ResultType->isSizelessVectorType()) && (!CondType->isExtVectorType() || ResultType->isExtVectorType()) && "Result should have been a vector type"' 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:7:38: current parser token ')'
2. /tmp/test.cpp:5:25: parsing function body 'mix_vector_types'
3. /tmp/test.cpp:5:25: in compound statement ('{}')
Stack dump without symbol names (ensure you have llvm-symbolizer in your PATH or set the environment var `LLVM_SYMBOLIZER_PATH` to point to it):
0 clang++ 0x000055f5d58690f9 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) + 121
1 clang++ 0x000055f5d5865dcc llvm::sys::RunSignalHandlers() + 76
2 clang++ 0x000055f5d5866678 llvm::sys::CleanupOnSignal(unsigned long) + 216
3 clang++ 0x000055f5d57a8f88
4 libc.so.6 0x00007f9cff9b2520
5 libc.so.6 0x00007f9cffa069fc pthread_kill + 300
6 libc.so.6 0x00007f9cff9b2476 raise + 22
7 libc.so.6 0x00007f9cff9987f3 abort + 211
8 libc.so.6 0x00007f9cff99871b
9 libc.so.6 0x00007f9cff9a9e96
10 clang++ 0x000055f5d8661d4a clang::Sema::CheckVectorConditionalTypes(clang::ActionResult&, clang::ActionResult&, clang::ActionResult&, clang::SourceLocation) + 2218
11 clang++ 0x000055f5d8681b69 clang::Sema::CXXCheckConditionalOperands(clang::ActionResult&, clang::ActionResult&, clang::ActionResult&, clang::ExprValueKind&, clang::ExprObjectKind&, clang::SourceLocation) + 1273
12 clang++ 0x000055f5d85ad390 clang::Sema::ActOnConditionalOp(clang::SourceLocation, clang::SourceLocation, clang::Expr*, clang::Expr*, clang::Expr*) + 192
13 clang++ 0x000055f5d807c527 clang::Parser::ParseRHSOfBinaryExpression(clang::ActionResult, clang::prec::Level) + 2647
14 clang++ 0x000055f5d807ed7d clang::Parser::ParseExpression(clang::TypoCorrectionTypeBehavior) + 13
15 clang++ 0x000055f5d8082f7d clang::Parser::ParseParenExpression(clang::ParenParseOption&, bool, clang::ParenExprKind, clang::TypoCorrectionTypeBehavior, clang::OpaquePtr&, clang::SourceLocation&) + 1661
16 clang++ 0x000055f5d8078f91 clang::Parser::ParseCastExpression(clang::CastParseKind, bool, bool&, clang::TypoCorrectionTypeBehavior, bool, bool*) + 2161
17 clang++ 0x000055f5d807aa7b clang::Parser::ParseCastExpression(clang::CastParseKind, bool, clang::TypoCorrectionTypeBehavior, bool, bool*) + 59
18 clang++ 0x000055f5d807ab1d clang::Parser::ParseAssignmentExpression(clang::TypoCorrectionTypeBehavior) + 61
19 clang++ 0x000055f5d807ed7d clang::Parser::ParseExpression(clang::TypoCorrectionTypeBehavior) + 13
20 clang++ 0x000055f5d810ef81 clang::Parser::ParseExprStatement(clang::Parser::ParsedStmtContext) + 81
21 clang++ 0x000055f5d8106b7b clang::Parser::ParseStatementOrDeclarationAfterAttributes(llvm::SmallVector&, clang::Parser::ParsedStmtContext, clang::SourceLocation*, clang::ParsedAttributes&, clang::ParsedAttributes&, clang::LabelDecl*) + 5547
22 clang++ 0x000055f5d810754b clang::Parser::ParseStatementOrDeclaration(llvm::SmallVector&, clang::Parser::ParsedStmtContext, clang::SourceLocation*, clang::LabelDecl*) + 363
23 clang++ 0x000055f5d810f7f7 clang::Parser::ParseCompoundStatementBody(bool) + 1639
24 clang++ 0x000055f5d811004f clang::Parser::ParseFunctionStatementBody(clang::Decl*, clang::Parser::ParseScope&) + 207
25 clang++ 0x000055f5d800332f clang::Parser::ParseFunctionDefinition(clang::ParsingDeclarator&, clang::Parser::ParsedTemplateInfo const&, clang::LateParsedAttrList*) + 2559
26 clang++ 0x000055f5d804ceb4 clang::Parser::ParseDeclGroup(clang::ParsingDeclSpec&, clang::DeclaratorContext, clang::ParsedAttributes&, clang::Parser::ParsedTemplateInfo&, clang::SourceLocation*, clang::Parser::ForRangeInit*) + 5140
27 clang++ 0x000055f5d7ffc15c clang::Parser::ParseDeclOrFunctionDefInternal(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec&, clang::AccessSpecifier) + 924
28 clang++ 0x000055f5d7ffc92f clang::Parser::ParseDeclarationOrFunctionDefinition(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*, clang::AccessSpecifier) + 959
29 clang++ 0x000055f5d80087a1 clang::Parser::ParseExternalDeclaration(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*) + 977
30 clang++ 0x000055f5d80097df clang::Parser::ParseTopLevelDecl(clang::OpaquePtr&, clang::Sema::ModuleImportState&) + 575
31 clang++ 0x000055f5d7fe670a clang::ParseAST(clang::Sema&, bool, bool) + 586
32 clang++ 0x000055f5d655f071 clang::FrontendAction::Execute() + 65
33 clang++ 0x000055f5d64e8c65 clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) + 1589
34 clang++ 0x000055f5d663aea3 clang::ExecuteCompilerInvocation(clang::CompilerInstance*) + 467
35 clang++ 0x000055f5d423dc96 cc1_main(llvm::ArrayRef, char const*, void*) + 7046
36 clang++ 0x000055f5d4233a2a
37 clang++ 0x000055f5d4233bbf
38 clang++ 0x000055f5d627035d
39 clang++ 0x000055f5d57a93a0 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref) + 160
40 clang++ 0x000055f5d62711b3
41 clang++ 0x000055f5d6226987 clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const + 167
42 clang++ 0x000055f5d622b1e0 clang::driver::Compilation::ExecuteJobs(clang::driver::JobList const&, llvm::SmallVectorImpl>&, bool) const + 304
43 clang++ 0x000055f5d6238e44 clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl>&) + 404
44 clang++ 0x000055f5d42392d3 clang_main(int, char**, llvm::ToolContext const&) + 7267
45 clang++ 0x000055f5d418b7a1 main + 113
46 libc.so.6 0x00007f9cff999d90
47 libc.so.6 0x00007f9cff999e40 __libc_start_main + 128
48 clang++ 0x000055f5d4233055 _start + 37
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 aefba88f46a6e55645c848f58f6ba56944d5ae62)
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-61a6ee.cpp
clang++: note: diagnostic msg: /tmp/test-61a6ee.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 aefba88f46a6e55645c848f58f6ba56944d5ae62)
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)*

Reproduce the crash with the supplied test.cpp and clang++ command, then inspect clang/lib/Sema/SemaExprCXX.cpp around CheckVectorConditionalTypes at the assertion shown in the report. Determine why the conditional expression leaves an invalid result type; done means the reproducer no longer aborts and emits a normal diagnostic or valid compilation result.

Written by the indexing model from the issue text.