Avoid hardcoding paths in Profile and Sys (#59998)
Current code fails when using custom paths. Save directory where Julia
source is stored during build in `SOURCEDIR` instead of assuming it can
be computed from `BINDIR` (new name chosen to avoid confusing with
`build_dir` which is different). Use `DATAROOTDIR` and `DATAROOT`
instead of hardcoding `usr/share/` and `share/`.
Fix/continuation of #56601, #56627.
