I am a total noob in Eclipse.
Today I have spent a few unpleasant minutes trying to solve Eclipse build issue.
I have invoked NVIC_Init() in my initialization code to configure timer interrupt.
For some weird reason linker failed: with "undefined reference to `NVIC_Init'".
After some painful minutes I found a thread on eclipse forum that solved the issue for me.
It appears that part of source files appear with "Exclude from build" flag by default. Unchecking that flag for stm32f0xx_misc.c solved the problem. Note also that project icons for included/excluded build files are different.