Some compilation failures result in nasty errors

e.g. with LLVM.jl on the `breaking changes` PR but GPUCompiler/CUDA.jl not, CUDA.jl gives:

```
ERROR: LoadError: LoadError: AssertionError: Core.Compiler.haskey(wvc, mi)
Stacktrace:
[1] ci_cache_populate(interp::GPUCompiler.GPUInterpreter, cache::GPUCompiler.CodeCache, mt::Nothing, mi::Core.MethodInstance, min_world::UInt64, max_world::Int32)
@ GPUCompiler ~/Julia/pkg/GPUCompiler/src/jlgen.jl:284
[2] compile_method_instance(job::GPUCompiler.CompilerJob, method_instance::Core.MethodInstance)
@ GPUCompiler ~/Julia/pkg/GPUCompiler/src/jlgen.jl:327
[3] macro expansion
@ ~/Julia/depot/packages/TimerOutputs/PZq45/src/TimerOutput.jl:226 [inlined]
[4] irgen(job::GPUCompiler.CompilerJob, method_instance::Core.MethodInstance)
@ GPUCompiler ~/Julia/pkg/GPUCompiler/src/irgen.jl:4
[5] macro expansion
@ ~/Julia/pkg/GPUCompiler/src/driver.jl:149 [inlined]
[6] macro expansion
@ ~/Julia/depot/packages/TimerOutputs/PZq45/src/TimerOutput.jl:226 [inlined]
[7] macro expansion
@ ~/Julia/pkg/GPUCompiler/src/driver.jl:148 [inlined]
[8] emit_llvm(job::GPUCompiler.CompilerJob, method_instance::Any; libraries::Bool, deferred_codegen::Bool, optimize::Bool, only_entry::Bool)
@ GPUCompiler ~/Julia/pkg/GPUCompiler/src/utils.jl:62
[9] codegen(output::Symbol, job::GPUCompiler.CompilerJob; libraries::Bool, deferred_codegen::Bool, optimize::Bool, strip::Bool, validate::Bool, only_entry::Bool, parent_job::Nothing)
@ GPUCompiler ~/Julia/pkg/GPUCompiler/src/driver.jl:58
[10] emit_function!(mod::LLVM.Module, job::GPUCompiler.CompilerJob, f::Function, method::GPUCompiler.Runtime.RuntimeMethodInstance)
@ GPUCompiler ~/Julia/pkg/GPUCompiler/src/rtlib.jl:68
[11] build_runtime(job::GPUCompiler.CompilerJob, ctx::LLVM.Context)
@ GPUCompiler ~/Julia/pkg/GPUCompiler/src/rtlib.jl:114
```

Reproduce the failure described with LLVM.jl on the breaking-changes PR while GPUCompiler and CUDA.jl are mismatched. Start in src/jlgen.jl at ci_cache_populate and follow the stack through src/irgen.jl, src/driver.jl, src/utils.jl, and src/rtlib.jl. Done means compilation failures report a useful error instead of the shown assertion, with regression coverage if an existing test location is identified.

Written by the indexing model from the issue text.