Do not emit single LLVM IR file for release mode + LTO none

[tanishiking]

fix #3502

This performance hack seems to be introduced when
there's no LTO option is available in scala-native (or LLVM at that time?)
#506

Am I correct that it's ok to remove this performance hack since we now have LTO option that optimize the LLVM IR by LTO option?

[WojciechMazur]

Am I correct that it's ok to remove this performance hack since we now have LTO option that optimize the LLVM IR by LTO option?

Yes, but mostly because combination of release+no lto leads to very bad development experience. Enoromous build times, are not a good trade for not that big performance improvement.
LTO is recommended for all release builds, but we cannot enable it by default - mostly becouse of problems on MacOs machines.

[LeeTibbert]

@tanishiking

Do you think this is a candidate to be ported back to the 0.4.n stream? If yes, could you try adding
a "Backport Candidate" (and probably a "component:build") label/labels. If GitHub will not let
you do that, yell and I'll add them.

Trying to get your/our good stuff into the hands of people who use it directly. BTW, thank you for
picking this off.

[tanishiking]

Hi @LeeTibbert I don't think this change can be a backport candidate to 0.4, because while I think important bugfixes should be backported to 0.4, this is an improvement of sorts. This improvement might motivate native Scala users to bump to 0.5. My two cents. Anyway, thank you for asking!