Do not let GCC use built-in functions

Do not let GCC use built-in functions

In order to reduce the software dependency on the compiler, the project
is now compiled with the '-ffreestanding' flag. This is to prevent GCC
from replacing functions with more optimised versions. An example is
where GCC replaces a simple printf() with a puts().

Change-Id: I1973fe6957cd708e8432a0039af9d50e037bd884