Mangle a Vararg whose length is still a TypeVar

[vchuravy]

mangle_param repeats the element type N times for an NTuple, but N is a TypeVar rather than an integer whenever the length is still parametric — which is exactly what the UnionAll branch just above it leaves behind after unwrap_unionall. 1:t.N then throws:

MethodError: no method matching (::Colon)(::Int64, ::TypeVar)
  [1] mangle_param(t::Any, substitutions::Vector{Any}, top::Bool)
    @ GPUCompiler src/mangling.jl:126
  ...
  [8] mangle_sig(sig::Any)
    @ GPUCompiler src/mangling.jl:189
  [9] relocation_namespace
    @ src/relocation.jl:326 [inlined]
 [10] collect_julia_value_relocations!(job, mod, gv_to_value)
    @ GPUCompiler src/relocation.jl:338
 [11] irgen(job::GPUCompiler.CompilerJob)

Such a type is == to the unbounded Vararg{T}, so this mangles it the same way — NTuple{N,Int} where N and Tuple{Vararg{Int}} both give Tuple<>. A concrete count is unaffected.

This became reachable from any job once relocation_namespace started mangling every job's signature rather than only a kernel's: Enzyme.jl hits it on GPUCompiler 2.x (EnzymeAD/Enzyme.jl#3512) while compiling a signature that carries one of these types.

🤖 Generated with Claude Code

https://claude.ai/code/session_01XmMWGrDGbAaajpehN7cAhW

[codecov]

Codecov Report

❌ Patch coverage is 66.66667% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 85.42%. Comparing base (78fa65e) to head (87a6e40).

Files with missing lines	Patch %	Lines
src/mangling.jl	66.66%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #921   +/-   ##
=======================================
  Coverage   85.41%   85.42%           
=======================================
  Files          29       29           
  Lines        5582     5583    +1     
=======================================
+ Hits         4768     4769    +1     
  Misses        814      814           

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