There is a static dependency in the test system for
this file. To prevent the issue from happening, move
the definition to the end of file so that the last
return in the main remains in the same line.
The idea is to use the simple program that is expected to be modified
rarely to set a breakpoint in a specific line and check that the
function mbedtls_zeroize() does actually set the buffer to 0 and is not
optimised out by the compiler.
