Move glue layer to dmd.ir

[wilzbach]

Motivation

• Makes it clear what the glue layer is and is to find where it's called
• The DMD as a library shouldn't need to access dmd.ir - this makes it explicit
• To keep things simple, this PR just moves the files - dmd.ir.glue_layer and dmd.ir.objc_glue are still required by the frontend

Script

replacements=(
"dmsc"
"e2ir"
"eh"
"glue"
"gluelayer"
"iasm"
"irstate"
"objc_glue"
"s2ir"
"tocsym"
"toctype"
"tocvdebug"
"todt"
"toir"
"toobj"
)
shopt -s globstar

for r in "${replacements[@]}" ; do
    w=($r)
    sed "s/dmd\.${w[0]}/dmd.ir.${w[0]}/g" -i **/*.d
done

[dlang-bot]

Thanks for your pull request, @wilzbach!

Bugzilla references

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[rainers]

You seem to have missed dmd.irstate in your replacement list.

[WalterBright]

No, I do not wish to split dmd up into lots of packages. I find it far more convenient to use a flat structure. The only reason root is separate is because it was originally intended to be a separate library. backend simply has to be separated.