Expose native_code's jl_sysimg_gvars.

[maleadt]

#57010 overhauled how global variables are initialized in code, breaking GPUCompiler.jl. After talking to @vtjnash, we are apparently supposed to use jl_get_llvm_gvs now to get the Julia memory location of a global variable (for a binding or constant value), however, the elements in there don't exactly correspond to the global variables in the module (not all module globals are "managed" by Julia, and the order is different).

To make GPUCompiler.jl work again, here I propose renaming jl_get_llvm_gvs to jl_get_llvm_gv_inits, and making jl_get_llvm_gvs instead return the list of the managed global variables, making it possible to perform the global variable initialization that was done by Julia before using something like:

if VERSION >= v"1.13.0-DEV.533"
    num_gvars = Ref{Csize_t}(0)
    @ccall jl_get_llvm_gvs(native_code::Ptr{Cvoid}, num_gvars::Ptr{Csize_t},
                           C_NULL::Ptr{Cvoid})::Nothing
    gvs = Vector{Ptr{LLVM.API.LLVMOpaqueValue}}(undef, num_gvars[])
    @ccall jl_get_llvm_gvs(native_code::Ptr{Cvoid}, num_gvars::Ptr{Csize_t},
                           gvs::Ptr{LLVM.API.LLVMOpaqueValue})::Nothing
    inits = Vector{Ptr{Cvoid}}(undef, num_gvars[])
    @ccall jl_get_llvm_gv_inits(native_code::Ptr{Cvoid}, num_gvars::Ptr{Csize_t},
                                inits::Ptr{Cvoid})::Nothing

    for (gv_ref, init) in zip(gvs, inits)
        gv = GlobalVariable(gv_ref)
        ptr = const_inttoptr(ConstantInt(Int64(init)), value_type(gv))
        initializer!(gv, ptr)
        obj = Base.unsafe_pointer_to_objref(init)
        @safe_info "Resolved $(name(gv)) to $obj"
    end
end

[gbaraldi]

Locations seems a bit odd, I was thinking something like values? Or inits? Just to make it clear it's actually a list of jl_value_t*s. But naming aside LGTM

[maleadt]

Yeah "locations" is a bit odd, but "global value values" seemed redundant while "inits" is specific to my use case. But I don't care about the name, so let's see what @vtjnash suggests.

[vchuravy]

I think inits is the correct wording, these are the initializer values of the global values.

[maleadt]

OK, renamed to inits.

[maleadt]

@vtjnash Bump.