False-positive with code using `@ccallable`

[Steve Kelly]

Consider the following, using PackageCompiler's MyLib example:

module MyLib

export increment32, increment64

function increment(count)
    count += 1
    return count
end

Base.@ccallable function increment32(count::Cint)::Cint
    count = increment(count)
    println("Incremented count: $count (Cint)")
    return count
end

Base.@ccallable function increment64(count::Clong)::Clong
    count = increment(count)
    println("Incremented count: $count (Clong)")
    return count
end

end

and the following JET report:

sjkelly@deepsea4:~/.julia/dev/PackageCompiler/examples/MyLib (sjk/flag_api1=)$ julia --project
               _
   _       _ _(_)_     |  Documentation: https://docs.julialang.org
  (_)     | (_) (_)    |
   _ _   _| |_  __ _   |  Type "?" for help, "]?" for Pkg help.
  | | | | | | |/ _` |  |
  | | |_| | | | (_| |  |  Version 1.10.0 (2023-12-25)
 _/ |\__'_|_|_|\__'_|  |  Official https://julialang.org/ release
|__/                   |

julia> using JET

julia> using MyLib
Precompiling MyLib
  1 dependency successfully precompiled in 1 seconds

julia> JET.report_package(MyLib)
[toplevel-info] virtualized the context of Main (took 0.011 sec)
[toplevel-info] entered into /home/sjkelly/.julia/dev/PackageCompiler/examples/MyLib/src/MyLib.jl
[toplevel-info]  exited from /home/sjkelly/.julia/dev/PackageCompiler/examples/MyLib/src/MyLib.jl (took 1.007 sec)
═════ 2 toplevel errors found ═════
┌ @ /home/sjkelly/.julia/dev/PackageCompiler/examples/MyLib/src/MyLib.jl:10 
│ @ccallable was already defined for this method name
│ Stacktrace:
│  [1] _ccallable(rt::Type, sigt::Type)
│    @ Base ./c.jl:513
└──────────────────────
┌ @ /home/sjkelly/.julia/dev/PackageCompiler/examples/MyLib/src/MyLib.jl:16 
│ @ccallable was already defined for this method name
│ Stacktrace:
│  [1] _ccallable(rt::Type, sigt::Type)
│    @ Base ./c.jl:513
└──────────────────────

This appears to be a false positive, and at least have an unclear fix considering this is standard code to interface with C. Is @ccallable doing something strange to the method tables?