compile-time import

[alexiss]

Hi, guys!

I'm writing a library that helps in embedded programming. The idea is to make a 
bunch of macros that expands into MCU-specific registers access. For example 
for STM32:
    
    
    mcu.RCC.AHBENR["IOPAEN"] = 1
    
    
    Run

I have a working sekelton now but I get a problem when try to do a 
cross-compilation for arm with `--os:standalone` option. My library actively 
uses `os` and other imports to find proper register definitions for specific 
MCU. All functions used for this are marked with `{.compileTime.}` pragma. But 
when I try to compile with `--os:standalone` I get following error:
    
    
    Error: OS module not ported to your operating system!
    
    
    Run

Is it possible in nim to import some libs only for compile-time stuff and not 
for target code?

Thanks in advance!