Clang ICE when casting between vector types with same size but different element types (long double → double)

### Link for quick verification: https://godbolt.org/z/566M875G7
```c
typedef long double __attribute__((__vector_size__(16))) V;
typedef double __attribute__((__vector_size__(16))) W;

W foo(V t) {
return (W)t; // Direct cast from V to W
}
```
Go back to `clang 2.7.0 (assertions)`. May relate to [63548](https://github.com/llvm/llvm-project/issues/63548).
The crash happens in IR generation (`CGExprScalar.cpp`) when creating a `CastInst` for the vector-to-vector conversion.
## Stack dump:
```console
clang++: /root/llvm-project/llvm/lib/IR/Instructions.cpp:3041: static llvm::CastInst* llvm::CastInst::Create(llvm::Instruction::CastOps, llvm::Value*, llvm::Type*, const llvm::Twine&, llvm::InsertPosition): Assertion `castIsValid(op, S, Ty) && "Invalid cast!"' 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. :8:3: LLVM IR generation of declaration 'foo'
3. :8:3: Generating code for declaration 'foo'
#0 0x00000000042ecc08 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x42ecc08)
#1 0x00000000042ea034 llvm::sys::CleanupOnSignal(unsigned long) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x42ea034)
#2 0x000000000422edd8 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
#3 0x000074d4cee42520 (/lib/x86_64-linux-gnu/libc.so.6+0x42520)
#4 0x000074d4cee969fc pthread_kill (/lib/x86_64-linux-gnu/libc.so.6+0x969fc)
#5 0x000074d4cee42476 gsignal (/lib/x86_64-linux-gnu/libc.so.6+0x42476)
#6 0x000074d4cee287f3 abort (/lib/x86_64-linux-gnu/libc.so.6+0x287f3)
#7 0x000074d4cee2871b (/lib/x86_64-linux-gnu/libc.so.6+0x2871b)
#8 0x000074d4cee39e96 (/lib/x86_64-linux-gnu/libc.so.6+0x39e96)
#9 0x0000000003ba97d6 (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3ba97d6)
#10 0x00000000046b7bfb llvm::IRBuilderBase::CreateCast(llvm::Instruction::CastOps, llvm::Value*, llvm::Type*, llvm::Twine const&, llvm::MDNode*, llvm::FMFSource) (.constprop.0) CGExprScalar.cpp:0:0
#11 0x00000000046d3bcc (anonymous namespace)::ScalarExprEmitter::VisitCastExpr(clang::CastExpr*) CGExprScalar.cpp:0:0
#12 0x00000000046caf26 clang::StmtVisitorBase::Visit(clang::Stmt*) CGExprScalar.cpp:0:0
#13 0x00000000046cd12b (anonymous namespace)::ScalarExprEmitter::Visit(clang::Expr*) CGExprScalar.cpp:0:0
#14 0x00000000046d376b (anonymous namespace)::ScalarExprEmitter::VisitCastExpr(clang::CastExpr*) CGExprScalar.cpp:0:0
#15 0x00000000046caee8 clang::StmtVisitorBase::Visit(clang::Stmt*) CGExprScalar.cpp:0:0
#16 0x00000000046d052c clang::CodeGen::CodeGenFunction::EmitScalarExpr(clang::Expr const*, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x46d052c)
#17 0x00000000047eded4 clang::CodeGen::CodeGenFunction::EmitReturnStmt(clang::ReturnStmt const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x47eded4)
#18 0x00000000047f72ad clang::CodeGen::CodeGenFunction::EmitStmt(clang::Stmt const*, llvm::ArrayRef) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x47f72ad)
#19 0x00000000047ff5cb clang::CodeGen::CodeGenFunction::EmitCompoundStmtWithoutScope(clang::CompoundStmt const&, bool, clang::CodeGen::AggValueSlot) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x47ff5cb)
#20 0x000000000486760e clang::CodeGen::CodeGenFunction::EmitFunctionBody(clang::Stmt const*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x486760e)
#21 0x0000000004878a64 clang::CodeGen::CodeGenFunction::GenerateCode(clang::GlobalDecl, llvm::Function*, clang::CodeGen::CGFunctionInfo const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4878a64)
#22 0x00000000048e6950 clang::CodeGen::CodeGenModule::EmitGlobalFunctionDefinition(clang::GlobalDecl, llvm::GlobalValue*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x48e6950)
#23 0x00000000048e15f4 clang::CodeGen::CodeGenModule::EmitGlobalDefinition(clang::GlobalDecl, llvm::GlobalValue*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x48e15f4)
#24 0x00000000048e1dd3 clang::CodeGen::CodeGenModule::EmitGlobal(clang::GlobalDecl) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x48e1dd3)
#25 0x00000000048ed363 clang::CodeGen::CodeGenModule::EmitTopLevelDecl(clang::Decl*) (.part.0) CodeGenModule.cpp:0:0
#26 0x0000000004c50b79 (anonymous namespace)::CodeGeneratorImpl::HandleTopLevelDecl(clang::DeclGroupRef) ModuleBuilder.cpp:0:0
#27 0x0000000004c416a4 clang::BackendConsumer::HandleTopLevelDecl(clang::DeclGroupRef) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4c416a4)
#28 0x0000000006a089f4 clang::ParseAST(clang::Sema&, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6a089f4)
#29 0x0000000004c4df88 clang::CodeGenAction::ExecuteAction() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4c4df88)
#30 0x0000000004f44885 clang::FrontendAction::Execute() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4f44885)
#31 0x0000000004ec4b1e clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4ec4b1e)
#32 0x000000000503ec0d clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x503ec0d)
#33 0x0000000000de5b1c cc1_main(llvm::ArrayRef, char const*, void*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xde5b1c)
#34 0x0000000000ddc56a ExecuteCC1Tool(llvm::SmallVectorImpl&, llvm::ToolContext const&, llvm::IntrusiveRefCntPtr) driver.cpp:0:0
#35 0x0000000000ddc6ed int llvm::function_ref&)>::callback_fn&)>(long, llvm::SmallVectorImpl&) driver.cpp:0:0
#36 0x0000000004cc08d9 void llvm::function_ref::callback_fn>, std::__cxx11::basic_string, std::allocator>*, bool*) const::'lambda'()>(long) Job.cpp:0:0
#37 0x000000000422f274 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x422f274)
#38 0x0000000004cc0eef clang::driver::CC1Command::Execute(llvm::ArrayRef>, std::__cxx11::basic_string, std::allocator>*, bool*) const (.part.0) Job.cpp:0:0
#39 0x0000000004c819d2 clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4c819d2)
#40 0x0000000004c8297e clang::driver::Compilation::ExecuteJobs(clang::driver::JobList const&, llvm::SmallVectorImpl>&, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4c8297e)
#41 0x0000000004c89dd5 clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl>&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4c89dd5)
#42 0x0000000000de1f11 clang_main(int, char**, llvm::ToolContext const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xde1f11)
#43 0x0000000000c8cf64 main (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xc8cf64)
#44 0x000074d4cee29d90 (/lib/x86_64-linux-gnu/libc.so.6+0x29d90)
#45 0x000074d4cee29e40 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x29e40)
#46 0x0000000000ddc005 _start (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xddc005)
clang++: error: clang frontend command failed with exit code 134 (use -v to see invocation)
Compiler returned: 134
```

Reproduce the crash with the vector-cast example and begin in CGExprScalar.cpp, where the stack trace shows LLVM IR generation creating the cast. Check the resulting CastInst request against the assertion in llvm/lib/IR/Instructions.cpp; done means this input no longer aborts during IR generation and has defined compiler behavior.

Written by the indexing model from the issue text.