Fixed RTOS compilation for some targets

More details: https://github.com/mbedmicro/mbed/pull/472
Revert "Fixed crash issue in RawSerial::printf for uARM"

This reverts commit d05b7f51d8db8b8081e1768b69802d992c20040c.

I am reverting this commit because:

- it uses alloca(), which is a dangerous function
- it uses vsprintf instead of vsnprintf, which can lead to a stack overflow.

Until we find a better solution, this might do more bad than good, so I am reverting it.
Fixed syntax error in build_release.py
Fixed RTOS compilation for some targets (in exporters)

More details: https://github.com/mbedmicro/mbed/pull/472
Merge branch 'master' of github.com:mbedmicro/mbed