Possibly omit debug information from non-debug HLTO files

[bbannier]

With #1092 we now omit debug information from Spicy and HILTI libraries in Release builds.

We should as a follow-up also omit debug information from HLTO files generated by e.g., spicyc and spicyz if Spicy itself was built without symbols (i.e., in Release mode). It looks like we might be able to achieve this by passing -s to the link step.

[rsmmr]

Should tie this to -d then: keep symbols if in debug mode.

[bbannier]

The tricky bit here seems to be that no matter what linker flags I try I still cannot remove as much information as strip. I am able to halve the size of an HTLO file, but any linker flag seems to only accomplish a fraction of that.