`llvmcall` segfaults if an argument has size 0

llvmcall catches incorrect argument types, but it doesn't catch arguments with empty bit representation (which are presumably not allowed in LLVM IR). I think it would be better if llvmcall threw an error in this case.

julia> f(x::T) where T = Base.llvmcall("ret i8 %0", Int8, Tuple{T}, x);

julia> f(1)
ERROR: Failed to parse LLVM assembly: 
<string>:2:8: error: '%0' defined with type 'i64' but expected 'i8'
ret i8 %0
       ^

julia> f(nothing)

[26746] signal 11 (1): Segmentation fault
in expression starting at REPL[3]:1
llvm_type_rewrite at /cache/build/tester-amdci4-14/julialang/julia-release-1-dot-12/src/ccall.cpp:407
emit_llvmcall at /cache/build/tester-amdci4-14/julialang/julia-release-1-dot-12/src/ccall.cpp:826
emit_intrinsic at /cache/build/tester-amdci4-14/julialang/julia-release-1-dot-12/src/intrinsics.cpp:1307
emit_call at /cache/build/tester-amdci4-14/julialang/julia-release-1-dot-12/src/codegen.cpp:5456
emit_expr at /cache/build/tester-amdci4-14/julialang/julia-release-1-dot-12/src/codegen.cpp:6383
emit_ssaval_assign at /cache/build/tester-amdci4-14/julialang/julia-release-1-dot-12/src/codegen.cpp:5870
emit_stmtpos at /cache/build/tester-amdci4-14/julialang/julia-release-1-dot-12/src/codegen.cpp:6172 [inlined]
emit_function at /cache/build/tester-amdci4-14/julialang/julia-release-1-dot-12/src/codegen.cpp:9347
[...]

Tested with Julia 1.12. Same with a few days old 1.13-nightly.

julia> versioninfo()
Julia Version 1.12.1
Commit ba1e628ee49 (2025-10-17 13:02 UTC)
Build Info:
  Official https://julialang.org release
Platform Info:
  OS: Linux (x86_64-linux-gnu)
  CPU: 4 × Intel(R) Core(TM) i3-10110U CPU @ 2.10GHz
  WORD_SIZE: 64
  LLVM: libLLVM-18.1.7 (ORCJIT, skylake)
  GC: Built with stock GC