ci: Strip debug info from host binaries

[abrodkin]

Some host utilities, namely *-gdb & *-lto-dump are insanely huge as they are built. But there's not much sense in them having extra 200+ MiB of debug data for a casual toolchain user, yet much slimmer toolchain both gets loaded from GitHub much faster and occupies much less space on the user's machine.

See results:

• Before: https://github.com/foss-for-synopsys-dwc-arc-processors/arc-gnu-toolchain/actions/runs/1960346303
• After: https://github.com/foss-for-synopsys-dwc-arc-processors/arc-gnu-toolchain/actions/runs/1964485947

                       before | after
=======================================
arc32-glibc-.tar.gz:   756 MB | 420 MB  
arc64-elf-.tar.gz:     394 MB | 247 MB  
arc64-glibc-.tar.gz:   765 MB | 425 MB