Add option to log which statement is being precompiled

[nickrobinson251]

We're seeing a hang during create_app (JuliaLang/julia#51603) for which we suspected a hang during type inference for a precompile(...) statement.

It these cases, it'd be helpful to be able to turn on a verbose/debug option to print which statement is being precompiled

There's a commented-out println in the code for this, so it'd just be turning that into a proper debug option

PackageCompiler.jl/src/PackageCompiler.jl

Line 343 in 846292c

# println(statement)