Use an early IR transform to replace GlobalRefs

[vchuravy]

julia> f() = (X;nothing)
f (generic function with 1 method)

julia> @code_lowered f()
CodeInfo(
1 ─     Main.X
└──     return Main.nothing
)

julia> native_code_typed(f, Tuple{})
static_eval(stmt) = Some([1, 2, 3])
1-element Vector{Any}:
 CodeInfo(
1 ─     return Main.nothing
) => Nothing

[codecov]

Codecov Report

Merging #311 (18470ee) into master (fa386cc) will decrease coverage by 0.51%.
The diff coverage is 53.84%.

@@            Coverage Diff             @@
##           master     #311      +/-   ##
==========================================
- Coverage   85.63%   85.11%   -0.52%     
==========================================
  Files          23       24       +1     
  Lines        2353     2392      +39     
==========================================
+ Hits         2015     2036      +21     
- Misses        338      356      +18     

Impacted Files	Coverage Δ
src/GPUCompiler.jl	100.00% <ø> (ø)
src/early_transform.jl	42.85% <42.85%> (ø)
src/jlgen.jl	80.21% <81.81%> (+0.10%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update fa386cc...18470ee. Read the comment docs.