importC with gc-sections not work on linux

[Dakota via Digitalmars-d-learn]

When I use importC to build a c library, there is a lot unused 
symbol missing.

I try add `-L--gc-sections` to dmd to workaround this issue.

I also try `-L-dead_strip` on macOS, it work as expected.


I do some google, some one suggestion use with 
`-ffunction-sections`, `-f fdata-sections`,  dmd seems not 
support it.


Any tips to work this around ?