Restructuring druntime

[Kagamin]

deimos
|-glibc
|---stdio.d
|---math.d
|---sys
|-----posix
|-bionic
|---stdio.d
|---math.d
|---sys
|-----posix
|-dietlibc
|---stdio.d
|---math.d
|---sys
|-----posix

Maybe better replicate c library structure?